III.

On the 29th of May, the engine called the "Samson" (weighing 10 tons 2 cwt., with 14-inch cylinders, and 16-inch stroke; wheels 4 feet 6 inches diameter, both pairs being worked by the engine; steam 50 lbs. pressure, 130 tubes) was attached to 50 waggons, laden with merchandise; net weight about 150 tons; gross weight, including waggons, 223 tons 6 cwt. The tender weighed 7 tons, making a gross load (including the engine) of 240 tons 8 cwt. The engine with this load travelled from Liverpool to Manchester (30 miles) in 2 hours and 40 min., exclusive of delays upon the road for watering, &c.; being at the rate of nearly 12 miles an hour. The speed varied according to the inclinations of the road. Upon a level, it was 12 miles an hour; upon a descent of 6 feet in a mile, it was 16 miles an hour; upon a rise of 8 feet in a mile, it was about 9 miles an hour. The weather was calm, the rails very wet; but the wheels did not slip, even in the slowest speed, except at starting, the rails being at that place soiled and greasy with the slime and dirt to which they are always exposed at the stations. The coke consumed in this journey, exclusive of what was raised in getting up the steam, was 1762 lbs., being at the rate of a quarter of a pound per ton per mile.

(195.) The great original cost, and the heavy expense of keeping the engines used on the railway in repair, have pressed severely on the resources of the undertaking. One of the best [Pg360] constructed of the later engines costs originally 1500_l._ and sometimes more. The original cost, however, is far from being the principal source of expense: the wear and tear of these machines, and the occasional fracture of those parts on which the greatest strain has been laid, have greatly exceeded what the directors had anticipated. Although this source of expense must be in part attributed to the engines not having yet attained that state of perfection, in the proportion and adjustment of their parts, of which they are susceptible, and to which experience alone can lead, yet there are some obvious defects which demand attention.

The heads of the boilers are flat, and formed of iron, similar to the material of the boilers themselves. The tubes which traverse the boiler were, until recently, copper, and so inserted into the flat head or end as to be water-tight. When the boiler was heated, the tubes were found to expand in a greater degree than the other parts of the boiler; which frequently caused them either to be loosened at the extremities, so as to cause leakage, or to bend from want of room for expansion. The necessity of removing and refastening the tubes caused, therefore, a constant expense.

It will be recollected that the fire-place is situated at one end of the boiler, immediately below the mouths of the tubes: a powerful draft of air, passing through the fire, carries with it ashes and cinders, which are driven violently through the tubes, and especially the lower ones, situated near the fuel. These tubes are, by this means, subject to rapid wear, the cinders continually

## acting upon their interior surface. After a short time it becomes

necessary to replace single tubes, according as they are found to be worn, by new ones; and it not unfrequently happens, when this is neglected, that tubes burst. After a certain length of time the engines require new tubing. This wear of the tubes might possibly be avoided by constructing the fire-place in a lower position, so as to be more removed from their mouths; or, still more effectually, by interposing a casing of metal, which might be filled with water, between the fire-place and those tubes which are the most exposed to the cinders and ashes. The unequal expansion of the tubes [Pg361] and boilers appears to be an incurable defect, if the present form of the engine be retained. If the fire-place and chimney could be placed at the same end of the boiler, so that the tubes might be recurved, the unequal expansion would then produce no injurious effect; but it would be difficult to clean the tubes, if they were exposed, as they are at present, to the cinders. The next source of expense arises from the wear of the boiler-heads, which are exposed to the action of the fire.

A considerable improvement was subsequently introduced into the method of tubing, by substituting brass for copper tubes. I am not aware that the cause of this improvement has been discovered; but it is certain, whatever be the cause, that brass tubes are subject to considerably slower wear than copper ones.

(196.) The expense of locomotive power having so far exceeded what was anticipated at the commencement of the undertaking, it was thought advisable, about the beginning of the year 1834, to institute an inquiry into the causes which produced the discrepancy between the estimated and actual expenses, with a view to the discovery of some practical means by which they could be reduced. The directors of the company, for this purpose, appointed a sub-committee of their own body, assisted by Mr. Booth, their treasurer, to inquire and report respecting the causes of the amount of this item of their expenditure, and to ascertain whether any and what measures could be devised for the attainment of greater economy. A very able and satisfactory report was made by this committee, or, to speak more correctly, by Mr. Booth.

It appears that, previous to the establishment of the railway, Messrs. Walker and Rastrick, engineers, were employed by the company to visit various places where steam power was applied on railways, for the purpose of forming an estimate of the probable comparative expense of working the railway by locomotive and by fixed power. These engineers recommended the adoption of locomotive power; and their estimate was, that the transport might be effected at the rate of ·278 of a penny, or very little more than a farthing per ton per mile. In the year [Pg362] 1833, five years after this investigation took place, it was found that the actual cost was ·625 of a penny, or something more than a halfpenny, per ton per mile, being considerably above double the estimated rate. Mr. Booth very properly directed his inquiries to ascertain the cause of this discrepancy, by comparing the various circumstances assumed by Messrs. Walker and Rastrick, in making their estimate, with those under which the transport was actually effected. The first point of difference which he observed was the _speed_ of transport: the estimate was founded on an assumed speed of ten miles an hour, and it was stated that a four-fold speed would require an addition of 50 per cent. to the power, without taking into account wear and tear. Now, the actual speed of transport being double the speed assumed in the statement, Mr. Booth holds it to be necessary to add 25 per cent. on that score.

The next point of difference is in the amount of the loads: the estimate is founded upon the assumption, that every engine shall start with its full complement of load, and that with this it shall go the whole distance. "The facts, however, are," says Mr. Booth, "that, instead of a _full load_ of profitable carriage _from_ Manchester, about half the waggons _come back empty_; and, instead of the tonnage being conveyed the whole way, many thousand tons are conveyed only half the way; also, instead of the daily work being uniform, it is extremely fluctuating." It is further remarked, that in order to accomplish the transport of goods from the branches and from intermediate places, engines are despatched several times a-day, from both ends of the line, _to clear the road_; the object of this arrangement being rather to lay the foundation of a beneficial intercourse in future, than with a view to any immediate profit. Mr. Booth makes a rough estimate of the disadvantages arising from these circumstances, by stating them at 33 per cent. in addition to the original estimate.

The next point of difference is the fuel. In the original estimate, _coal_ is assumed as the fuel, and it is taken at the price of five shillings and ten-pence per ton: now the act of parliament forbids the use of coal which would produce smoke; the company have, therefore, been obliged to use _coke_, at [Pg363] seventeen shillings and sixpence a ton.[32] Taking coke, then, to be equivalent to coal, ton for ton, this would add ·162 to the original estimate.

These several discrepancies being allowed for, and a proportional amount being added to the original estimate, the amount would be raised to ·601 of a penny per ton per mile, which is within one fortieth of a penny of the actual cost. This difference is considered to be sufficiently accounted for by the wear and tear produced by the very rapid motion, more especially when it is considered that many of the engines were constructed before the engineer was aware of the great speed that would be required.

"What, then," says Mr. Booth, in the Report already alluded to, "is the result of these opposite and mutually counteracting circumstances? and what is the present position of the company in respect of their moving power? Simply, that they are still in a course of experiment, to ascertain practically the best construction, and the most durable materials, for engines required to transport greater weights, and at greater velocities, than had, till very recently, been considered possible; and which, a few years ago, it had not entered into the imagination of the most daring and sanguine inventor to conceive: and farther, that these experiments have necessarily been made, not with the calm deliberation and quiet pace which a salutary caution recommends,—making good each step in the progress of discovery before advancing another stage,—but amidst the bustle and responsibilities of a large and increasing traffic; the directors being altogether ignorant of the time each engine would last before it would be laid up as inefficient, but compelled to have engines, whether good or bad; being aware of various defects and imperfections, which it was impossible at the time to remedy, yet obliged to keep the machines in motion, under all the disadvantages of heavy repairs, constantly going on during the night, in order that the requisite number of engines might be ready for the morning's work. Neither is this great experiment yet complete; it is still going forward. But the most prominent difficulties have been in a great measure surmounted, [Pg364] and your committee conceive that they are warranted in expecting, that the expenditure in this department will, ere long, be materially reduced,—more especially when they consider the relative performances of the engines at the _present time_, compared with what it was two years ago."

In the half year ending 31st December, 1831, the six best engines performed as follows:—

Miles. Planet 9,986 Mercury 11,040 Jupiter 11,618 Saturn 11,786 Venus 12,850 Etna 8,764 —————— Making in all 66,044 ——————

In the half year ending 31st December, 1833, the six best engines performed as follows:—

Miles. Jupiter 16,572 Saturn 18,678 Sun 14,552 Etna 17,763 Ajax 11,678 Firefly 15,608 —————— Making in all 95,851 ——————

(197.) Since the date to which the preceding observations refer, the locomotive engine has undergone several improvements in detail of considerable importance; among which, the addition of a third pair of wheels deserves to be particularly mentioned. An engine supported on three pair of wheels has great security in the event of the fracture of any one of the axles,—the remaining axles and wheels being sufficient for the support of the machine. Connected with this change is another, recommended by Mr. Robert Stephenson, by which the flanges are removed from the driving wheels, those upon the remaining pairs of wheels being sufficient to keep the engine in its position upon the rails. We shall now describe a locomotive engine similar in construction to those almost [Pg365] universally used at present on railroads, as well in this kingdom as in other countries.[33]

The external appearance of the engine and tender is shown in the engraving at the head of this chapter. In _fig._ 97. is exhibited a vertical section of the engine made by a plane carried through its length; and in _fig._ 98. is exhibited a corresponding section of its tender,—the tender being supposed to be joined on to the engine at the part where the connecting points appear to be broken in the drawing. In _fig._ 99. is exhibited the plan of the working machinery, including the cylinders, pistons, eccentrics, &c. which are under the boiler, by the operation of which the engine is driven. _Fig._ 100. represents the tender, also taken in plan.

In _fig._ 101. is represented an elevation of the hinder end of the engine next the fire-box; and in _fig._ 102. is represented a cross vertical section through the fire-box, and at right angles to the length of the engine, showing the interior of the boiler above and beside the fire-box, the rivets and bolts connecting the internal and external fire-boxes, the regulator, steam funnel, and steam dome.

In _fig._ 103. is represented an elevation of the front of the engine next the smoke-box, showing the cylinder covers W, buffers T, &c.; and in _fig._ 104. is represented a section of the interior of the smoke-box, made by a vertical plane at right angles to the engine, showing the tube plate forming the foremost end of the boiler, the branches S of the steam-pipe leading to the cylinders, the blast-pipe _p_, the cylinders H, and the chimney G.

The same letters of reference are placed at corresponding parts in the different figures.

The boiler, as has been explained in the engines already described, is a cylinder placed upon its side, the section of which is exhibited at A, _fig._ 97. The fire-box consists of two casings of metal, one within the other. The fire-grate is represented at D. The tubes by which the products of combustion are [Pg366] drawn from the fire-box to the smoke-box F are represented at E. Upon the smoke-box is erected the chimney G. In the engine from which this drawing has been taken, and which was used on the London and Birmingham Railway, the boiler is a cylinder 7-1/2 feet long, and 3-1/2 feet in diameter. It is formed of wrought-iron plates 5/16 of an inch in thickness, overlapping each other, and bound together by iron rivets 7/8 of an inch in diameter and 1-3/4 inch apart. One of these rivets, as it joins two plates, is represented in _fig._ 95. The boiler is clothed with a boarding of wood _a_, an inch in thickness, and bound round by iron hoops screwed together at the bottom. Wood being a slow conductor of heat, this covering has the effect of keeping the boiler warm, and checking the condensation of steam which would otherwise be produced by the rapid motion of the engine through the cold air.

[Illustration: _Fig._ 95.]

[Illustration: _Fig._ 96.]

The external fire-box, B B, is a casing nearly square in its plan, being four feet wide outside, and three feet seven and a half inches long, measured in the direction of the boiler. It is constructed of wrought-iron plates, similar to those of the boiler. This box descends about two feet below the boiler, the top being semi-cylindrical, as seen in _fig._ 102., of a somewhat greater diameter than the boiler, and concentrical with it. The front of the fire-box next the end of the boiler has a circular opening equal in size to the end of the boiler. To the edge of this opening the boiler is fastened by angle irons, and rivets in the manner represented in _fig._ 96. These rivets are seen in section in _fig._ 97.

The internal fire-box C, _fig._ 97., is similar in shape to the external, only it is flat at the top, and close every where except at the bottom. Between it and the external fire-box an open space of three inches and a half is left all round, and on the side next the boiler this space is increased to four inches. This internal fire-box is made of copper plates, 7/16 [Pg367] of an inch in thickness, every where except next the boiler, where the thickness is 7/8.

As the sides and front of the external fire-box, and all the surfaces bounding the internal fire-box, are flat, their form is unfavourable for the resistance of pressure. Adequate means are, therefore, provided for strengthening them. The plates forming the internal fire-box are bent outwards near the bottom, until they are brought into contact with those of the external fire-box, to which they are attached by copper rivets, as represented at _f_ in _fig._ 97. The plates forming the bounding surfaces of the two fire-boxes are fastened together by stays represented at _k_ in _figs._ 97. and 102. These stays, which are of copper, have a screw cut upon them through their whole length, and holes are made through the plates of both fire-boxes tapped with corresponding threads. The copper screws are then passed through them, and rivets formed on their heads within and without, as seen in _fig._ 102. These screw rivets connect all parts of the plating of the two fire-boxes which are opposed to each other: they are placed at about four inches apart over the sides and back of the internal fire-place and that part of the front which is below the boiler.

[Illustration: _Fig._ 97.

LONGITUDINAL VERTICAL SECTION OF A LOCOMOTIVE ENGINE.]

[Illustration: _Fig._ 98.

LONGITUDINAL VERTICAL SECTION OF THE TENDER.]

[Illustration: _Fig._ 99.

PLAN OF THE WORKING MACHINERY OF A LOCOMOTIVE ENGINE.]

[Illustration: _Fig._ 100.

PLAN OF THE TENDER.]

[Illustration: _Fig._ 101.

ELEVATION OF THE HINDER END OF A LOCOMOTIVE ENGINE.]

[Illustration: _Fig._ 102.

CROSS VERTICAL SECTION OF THE ENGINE THROUGH THE FIRE-BOX.]

[Illustration: _Fig._ 103.

ELEVATION OF THE FOREMOST END OF THE ENGINE.]

[Illustration: _Fig._ 104.

CROSS VERTICAL SECTION OF ENGINE THROUGH THE SMOKE-BOX.]

As the top of the internal fire-box cannot be strengthened by stays of this kind, ribs of wrought-iron, which are seen in their length at _l_, in _fig._ 97., and of which an end view is seen in _fig._ 102., are attached by bolts to it. These ribs are hollowed out, as seen in _fig._ 97., between bolt and bolt, in order to break their contact with the roof of the fire-box, and allow a more free passage to the heat through it. If they were in continuous contact with the fire-box, the metal composing them would become more highly heated, and would soon wear out, besides intercepting heat from the water. This part of the fire-box is subject to rapid wear, unless care be taken that the level of the water be preserved at its proper height in the boiler. Even when the boiler is properly filled, the depth of water above the roof of the fire-box is not considerable, and on the least neglect the roof may be exposed to the contact of steam, in which case it will soon be destroyed.

To prevent accidents arising from this cause, a leaden plug, [Pg368] represented at _m_, _figs._ 97. and 102., is inserted in the roof of the internal fire-box. If the water be allowed to subside, this plug will melt out before the copper is very injuriously heated, and the steam rushing out at the aperture will cause the fire to be extinguished.

Copper fire-boxes are almost universally used; but sometimes, from the consideration of cheapness, the internal fire-box is constructed of iron.

In the plating which forms the back of the external fire-box, an oval aperture is formed, as represented in the back view of the engine, _fig._ 101., for the fire-door _g_. The plating of the internal fire-box around this aperture is bent at right angles to meet that of the external fire-box, to which it is fastened by a row of copper rivets. The fire-door is formed of two plates of wrought-iron, riveted together with a space of nine inches and a half between them. The air between these plates being an imperfect conductor of heat, keeps the outer plate of the fire-door at a moderate temperature.

In that part of the surface of the internal fire-box which forms the end of the boiler, holes are made to receive the extremities of the tubes, by which the air proceeding from the fire is drawn to the smoke-box at the remote end of the boiler. These tubes are represented in longitudinal section at E, _fig._ 97., and their ends are seen in the surface of the internal fire-box in _fig._ 102., and in the remote end of the boiler where they terminate in the smoke-box in _fig._ 104. These tubes are formed of the best rolled brass, and their thickness in the engine, to which we now refer, is 1/13 of an inch. After the brass plating is bent into the form of a tube, and being overlapped, is properly soldered together, and the edges smoothed off, the tubes are made perfectly cylindrical by being drawn through a circular steel die.

[Illustration: _Fig._ 105.]

The tube-plates (as those parts of the boiler ends in which the tubes are inserted are called) are bored with holes in corresponding positions, truly cylindrical, and corresponding in magnitude to the tubes, so that the tubes, when passed into them, will be just in contact with them. The length of the tubes is so regulated, that when extending from end to end of the boiler, and passing through the holes, they shall [Pg369] project at each end a little beyond the holes. The manner of fastening them so as to be water-tight is as follows:—A steel hoop or ferrule, made slightly conical, a section of which is exhibited at C. _fig._ 105., the smaller end of which is a little less than the internal diameter of the tube, but which increases towards the outer end, is driven in as represented in the figure. It acts as a wedge, and forces the tube into close contact with the edges of the hole in the tube-plate.

When particular tubes in a boiler are worn out, and require to be replaced, their removal is easily effected. It is only necessary to cut the steel ferrule on the inside, and to bend it off from contact with the tube, by which means it can be loosened and withdrawn, and the tube removed.

In the engine to which this description refers there were one hundred and twenty-four tubes, the external diameter of which was 1-5/8 inch. The distance between tube and tube was 3/4 of an inch. The number of tubes vary in different engines, some having so many as one hundred and fifty, while the number in some is less than ninety. The evaporating power of an engine greatly depends on the proper number and magnitude of its tubes; and the experience which engineers have had on railways have led them gradually to increase the number of tubes, and diminish their magnitude. In the Rocket, already mentioned as having gained the prize on the opening of the Liverpool and Manchester Railway, the number of tubes was twenty-four, and their diameter three inches; but in all the engines subsequently made their number was augmented, and their diameter diminished. The practical inconvenience which limits the size of the tubes is their liability to become choked by cinders and ashes, which get wedged in them when they are too small, and thereby obstruct the draft, and diminish the evaporating power of the boiler. The tubes now in use, of about an inch and a [Pg370] half internal diameter, not only require to be cleared of the ashes and cinders, which get fastened in them after each journey, but it is necessary throughout a journey of any length that the tubes should be picked and cleaned by opening the fire door at convenient intervals.

The substitution of brass for copper tubes, which has been already mentioned as so great an improvement in the construction of locomotive engines, is ascribed to Mr. Dixon, who suggested them in 1833, being then the resident engineer of the Liverpool and Manchester Railway. They are said to last six or eight times as long as copper tubes of the same dimensions.

When tubes fail, they are usually destroyed by the pressure of the water crushing them inwards: the water enters through the rent made in the tube, and flowing upon the fire extinguishes it. When a single tube thus fails upon a journey, the engine, notwithstanding the accident, may generally be made to work to the end of its journey by plugging the ends of the broken tube with hard wood; the water in contact with which will prevent the fire from burning it away.

Tubes of the dimensions here referred to weigh about sixteen pounds, and lose from six to seven pounds before they are worn out. Their cost is about one pound each.

The tubes act as stays, connecting the ends of the boiler to strengthen them. Besides these, there are rods of wrought iron extended from end to end of the boiler above the roof of the internal fire-place. These rods are represented at _o_ in their length in _fig._ 97., and an end view of them is seen in _fig._ 102. The smoke-box F, _fig._ 97. 104., containing the cylinders, steam-pipe, and blast-pipe, is four feet wide, and two feet long. It is formed of wrought iron plates, half an inch thick on the side next the boiler, and a quarter of an inch elsewhere. The plates are riveted in the same manner as those of the fire-box already described. From the top of the smoke-box, which, like the fire-box, is semi-cylindrical, as seen in elevation in _fig._ 103., and in section _fig._ 104., rises the chimney G, fifteen inches diameter, and formed of 1/8 inch iron plates, riveted and bound round by hoops. It is flanged to the top of the [Pg371] smoke-box, as represented in _fig._ 104. Near the bottom of the smoke-box the working cylinders are placed, side by side, in a horizontal position, with the slide valves upwards. In the top of the external fire-box a circular aperture is formed fifteen inches in diameter, and upon this aperture is placed the steam-dome T (_figs._ 97. 101, 102.) two feet high, and attached around the circular aperture by a flange and screw secured by nuts. This steam dome is made of brass 3/8 inch thick. In stationary boilers, where magnitude is not limited, it has been already explained, that the space allowed for steam is sufficiently large to secure the complete separation of the vapour from the spray which is mixed with it when it issues immediately from the water. In locomotive boilers sufficient space cannot be allowed for this, and the separation of the water from the steam is effected by the arrangement here represented. A funnel-shaped tube _d′_ (_figs._ 97. 102.), with its wide end upwards, rises into the steam-dome, and reaches nearly to the top of it. This funnel bends towards the back of the fire-box, and is attached by a flange and screws to the great steam-pipe S, which traverses the whole length of the boiler. The steam rising from the boiler fills the steam-dome T, and descends in the funnel-shaped tube _d′_. The space it has thus to traverse enables the steam to disengage itself almost completely from the priming. The wider part of the great steam-pipe _a_ is flanged and screwed at the hinder end to a corresponding aperture in the back plate of the fire-box. This opening is covered by a circular plate, secured by screws, having a stuffing-box in its centre, of the same kind as is used for the piston-rods of steam-cylinders. Through this stuffing-box the spindle _a″_ of the regulator passes, and to its end is attached a winch _h′_, by which the spindle _a″_ is capable of being turned. This winch is limited in its play to a quarter of a revolution. The other end of the spindle _a″_ is attached to a plate _e′_ seen edgeways in _fig._ 97., and the face of which is seen in _fig._ 102.: this circular plate _e_ is perforated with two apertures somewhat less than quadrants. That part of the plate, therefore, which remains not pierced forms two solid pieces somewhat greater than quadrants. This plate is ground so as to move in steam-tight [Pg372] contact with a fixed plate under it, which terminates at the wide end of the conical mouth of the steam-pipe S. This fixed circular plate is likewise pierced with two nearly quadrantal apertures, corresponding with those in the movable plate _e′_. When the movable plate _e′_ is turned round by the winch _h′_, the apertures in it may be made to correspond with those of the fixed circular plate on which it moves, in which position the steam-pipe S communicates with the funnel _d′_ by the two quadrantal apertures thus open. If, on the other hand, the winch _h′_ be moved from this position through a quarter revolution, then the quadrantal openings in the movable plate will be brought over the solid parts of the fixed plate on which it moves, and these solid parts being a little more than quadrants, while the openings are a little less, all communication between the steam-pipe S and the funnel _d′_ will be stopped, for in this case the quadrantal openings in the fixed and movable plates respectively will be stopped by the solid parts of these plates. It will be evident that as the winch _h′_ of the regulator is moved from the former position to the latter, in every intermediate position the aperture communicating between the funnel _d′_ and the steam-pipe S will be less in magnitude than the complete quadrant. It will in fact be composed of two openings having the form of _sectors_ of a circle less than a quadrant, and these sectors may be made of any magnitude, however small, until the opening is altogether closed.

By such means the admission of steam from the boiler to the steam-pipe S may be regulated by the winch _h′_.

The steam being admitted to the steam-pipe passes through it to the front end of the boiler, and the pipe being enclosed within the boiler the temperature of the steam is maintained. The steam-pipe passing through the tube-plate at the front end of the boiler is carried to a small distance from the tube-plate in the same direction, where it is flanged on to a cross horizontal pipe proceeding to the right and to the left as represented in _fig._ 104. This cross pipe is itself flanged to two curved steam-pipes S (_fig._ 104.), by which the steam is conducted to the valve-boxes V V. The lower ends of these curved arms are flanged on to the valve-boxes of the two cylinders [Pg373] at the ends nearest to the boiler. The opening of one of these is exhibited in the right hand cylinder in _fig._ 99. By these pipes the steam is conducted into the valve-boxes or steam-chests, from which it is admitted by slide-valves to the cylinders to work the pistons in the same manner as has been already described in the large stationary engines.

On the upper sides of the cylinders are formed the steam-chests or valve-boxes, which are exhibited at U (_figs._ 97. 99. 104.). These are made of cast-iron half an inch thick, and are bolted to the upper side of each cylinder. At the front end they are also secured by bolts to the smoke-box, and at the hinder end are attached to the tube-plate. These valve-boxes communicate with the passages _m_ and _n_ _fig._ 99. leading to the top and bottom of the cylinder: these are called the steam-ports. They also communicate with a passage _o_ leading to the mouth of a curved horizontal pipe _p′_ connecting the front ends of the two cylinders, as seen in _figs._ 99. 104. These curved pipes unite in a single vertical pipe _p_, called the _blast-pipe_, seen in _figs._ 97. 104.: this vertical pipe becomes gradually small towards the top, and terminates a little above the base of the funnel or chimney G. In the valve-box is placed the slide-valve _v_ to which is attached the spindle _l′_. This spindle moves through a stuffing-box _k′_, and is worked by gearing, which will be described hereafter. According to the position given to the slide, a communication may be opened between the steam-chest, or the waste-port, and either end of the cylinders. Thus when the slide is in the position represented in _fig._ 97. the steam-chest communicates with the front end of the cylinder, while the waste-port communicates with the hinder end. If, on the other hand, the spindle _l′_ being pressed forward, move the slide to its extreme opposite position, the steam-port _n_ would communicate with the waste-port _o_, while the steam-chest would communicate with the steam-port _m_, steam would, therefore, be admitted to the hinder end of the cylinder, while the foremost end would communicate with the waste-port. It will be perceived that this arrangement is precisely similar to that of the slide-valves already described (133.). The slide-valve is represented on a larger scale in _fig._ 106., where A is the hinder steam-port, [Pg374] B the foremost steam-port, and C the waste-port. The surfaces D, separating the steam-ports from the waste-ports, are called the bars: they are planed perfectly smooth, so that the surfaces F and G of the slide-valve, also planed perfectly smooth, may move in steam-tight contact with them. These surfaces are kept in contact by the pressure of the steam in the steam-chest, by which the slide-valve is always pressed down. In its middle position, as represented by the dotted lines in the figure, both the steam-ports are stopped by the slide-valve, so that at that moment no steam is admitted to either end of the cylinder. On either side of this intermediate position the slide has an inch and a half play, which is sufficient to open successively the two steam-ports.

[Illustration: _Fig._ 106.]

The cylinders are inserted at one end in the plate of the smoke-box, and at the other in the tube-plate of the boiler. They are closed at either end by cast iron covers, nearly an inch thick, flanged on by bolts and screws. In the cover of the cylinder attached to the tube-plate is a stuffing-box, in which the piston rod plays. The metallic pistons used in locomotive engines do not differ materially from those already described, and therefore need not be here particularly noticed. From their horizontal position they have a tendency to wear unequally in the cylinders, their weight pressing them on one side only; but from their small magnitude this effect is found to be imperceptible in practice. In the engine here described the stroke of the piston is eighteen inches, and this is the most usual length of stroke in locomotive engines. The piston, in its play, comes at either end within about half an inch of the inner surface of the covers of the cylinders, this space being allowed to prevent collision. In the foremost cover of the cylinder is inserted a cock _q′_ (_fig._ 97. 99.), by which any water which may collect in the cylinder by condensation or priming may be discharged. A cock _r′_ (_fig._ 97.), communicating with a small tube proceeding from the branches of the waste pipe _p′_ (_fig._ 104.), is likewise provided to discharge from that pipe any water which may be [Pg375] collected in it. After the steam has been admitted to work the piston through the slide-valve, and has been discharged through the waste-port by shifting that valve, it passes through the pipe _p′_ into the blast-pipe _p_, from the mouth of which it issues, with great force, up the funnel G. When the motion of the engine is rapid, the steam from the two cylinders proceeds in an almost uninterrupted current from the blast-pipe, and causes a strong draft up the chimney. The heated air which passes from the mouths of the tubes into the smoke-box is drawn up by this current, and a corresponding draft is produced in the fire-box.

[Illustration: _Fig._ 107.]

The piston-rods Y terminate in a fork, by which they are attached to cross heads Z, the ends of which are confined by guide-bars A′, in which they are allowed to play backwards and forwards through a space equal to the stroke of the piston. To these cross heads Z, between the prongs of the fork in which the piston terminates, are attached the foremost ends of the connecting rods B′. These rods are, therefore, driven backwards and forwards by the motion imparted to the cross head Z by the piston-rods Y. The connecting rods B′ are attached at the hinder ends to two cranks formed upon the axles C′ of the driving wheels D′. These two cranks are formed upon the axles precisely at right angles to each other. The left-hand crank is represented in its horizontal position, in _fig._ 99., and the right-hand crank is seen in its vertical position. A cranked axle is represented on a larger scale in _fig._ 107., and the two cranks are seen in a position oblique to the plane of the figure. As this axle is the instrument by which the impelling force is conveyed to the load, and as it has to support a great portion of the weight of the engine, it is constructed with great strength and precision. It is made all in one [Pg376] piece, and of the best wrought iron called Back Barrow, or scrap iron. In the engine here described its extreme length is six feet and a half, and its diameter is five inches. At the centre part A it is cylindrical, and is increased to five inches and a quarter at C, where the cranks are formed. The sides D of the cranks are four inches thick, and the crank pins B, which are truly cylindrical, are five inches diameter, and three inches in length, the brasses at the extremities of the connecting rods which play upon them having a corresponding magnitude. The distance from the centre of the crank-pins B to the centre of the axle A must be exactly equal to half the stroke of the piston, and is, therefore, in this case precisely nine inches. Upon the parts F, which are seven inches and a half long, the great driving wheels are firmly fastened, so as to be prevented from turning or shaking upon the axle. The axle projects beyond the wheels at G, where it is reduced to three inches and an eighth diameter. These projecting parts G are five inches long, having collars at the outer ends. Brasses are fixed at the outside frame of the engine which rest upon these projections G of the axle, and upon these brasses the weight of the engine is supported. The entire axle is accurately turned in a lathe, and each of the crank-pins B is likewise turned by suspending the axle on centres corresponding with the centres of the crank-pins, and made on strong cast iron arms, which are firmly fixed on the ends of the axle, and project beyond the cranks so as to balance the axle, and enable it to turn round on the centre of the crank-pin. The axle is by such means made perfectly true, and the cranks are made of exactly the proper length, and precisely at right angles to each other. The corners of the cranks are champered off, as shown in the figure, and the ends of the cylindrical parts well rounded out.

The strength and accuracy of construction indispensable in these cranked axles, in order to make them execute their work, render them very expensive. Those which are here described cost about 50_l._ each. When properly constructed, however, they are seldom broken, but are sometimes bent when the engine escapes from the rails.

The proper motion to admit and withdraw the steam from [Pg377] either end of the cylinder is imparted to the slide-valves by eccentrics, in a manner and on a principle so similar to that already described in large stationary engines, that it will not be necessary here to enter into any detailed explanation of the apparatus for communicating this motion, which is exhibited in plan and section in _figs._ 97. 99. The eccentrics are attached to the cranked axles at E′ E″. The eccentric E′ imparts motion by a rod _e″_ to a lever _h″_, formed on an axle extending across the frame of the engine. This conveys motion to another lever _l″_, projecting from the same axle. This lever _l″_ is jointed to horizontal links _m″_, which at the foremost ends are attached to the spindle _l′_, by which the slide is driven. By these means the motion received by the eccentric from the great working axle conveys to the spindle _l′_ an alternate movement backwards and forwards, and the points at which it is reversed will be regulated by the position given to the eccentric upon the great axle. The eccentric is formed in two separate semicircles, and is keyed on to the great axle, and consequently any position may be given to it which may be required. The position to be given to the eccentrics should be such that they shall be at right angles to their respective cranks, and they should be fixed a quarter of a revolution behind the cranks so as to move the slides to that extent in advance of the pistons, since by the position of the levers _h″_ and _l″_, the motion of the eccentric becomes reversed before it reaches the valve spindle.

The performance of the engine is materially affected by the position of the eccentrics on the working axle. The slide should begin to uncover the steam-port a little before the commencement of the stroke of the piston, in order that the steam impelling the piston should be shut off, and the steam about to impel it in the contrary direction admitted before the termination of the stroke. Through this small space the steam, therefore, must act in opposition to the motion of the piston. This is called the _lead_ of the slide, and the extent generally given to it is about a quarter of an inch. This is accomplished by fixing the eccentrics not precisely at right angles to the respective cranks, but a little in advance of that position. The introduction of the steam to [Pg378] the piston before the termination of the stroke has the effect of bringing it gradually to rest at the end of the stroke, and thereby diminishing the jerk or shock produced by the rapid change of motion. In stationary engines, where the reciprocations of the engine are slow, the necessity for this provision does not arise; but in locomotive engines in which the motion of the piston is changed from four to six times in a second, it becomes necessary. The steam admitted to the piston before the termination of the stroke acts as a spring-cushion to assist in changing its motion, and if it were not applied, the piston could not be kept tight upon the piston-rod. Another advantage which is produced by allowing some lead to the slide is that the waste steam which has just impelled the piston begins to make its escape through the waste-port before the commencement of the next stroke, so that when the impelling steam begins to produce the returning stroke, there is less waste steam on the other side of the piston to resist it.

When the motion of the engine is very rapid, the resistance of the waste steam, as it escapes from the blast-pipe to the piston, has been generally supposed to be very considerable, though we are not aware of any direct experiments by which its amount has been ascertained. In the account of the locomotive engine which has been here described, supplied by Mr. Stephenson for the last edition of Tredgold on the Steam Engine, he states, that the average resisting pressure of the waste steam throughout the stroke is 6 lbs. per square inch, when running at the usual rate of from 25 to 28 miles an hour, and that at greater velocities this negative pressure has been found to increase to more than double that amount. No experiments are, however, cited from which this inference has been drawn.

It has been also thought that the pressure of steam upon the piston in the cylinder, at high velocities, is considerably below the pressure of steam in the boiler; but this has not been, so far as we are informed, ascertained by any satisfactory experimental test. Mr. Stephenson likewise states, that this loss of pressure, causes the negative pressure or resistance of the waste steam to amount to [Pg379] from 30 to 40 per cent. of the positive pressure upon the piston when the engine is running very fast, and that therefore the power of the engine is diminished nearly one half.

But it will be perceived that besides the uncertainty which attends the estimate of the actual amount of pressure on the piston compared with the pressure of steam in the boiler, the inference here drawn does not appear to be compatible with what has been already proved respecting the mechanical effect of steam. No change of pressure which may take place between the boiler and the cylinder can affect the practical efficacy of the steam. As the steam passes through the engine, whatever change of pressure it may be subject to, it still remains common steam; and though its pressure may be diminished, its volume being increased in a nearly equal proportion, its mechanical effect will remain the same. The power of the engine, therefore, estimated as it ought to be, by the whole mechanical effect produced, will not be altered otherwise than by the effect of the increased resistance produced by the blast-pipe. What that resistance is, we repeat, has not, so far as we know, been ascertained by direct experiment, and there are circumstances attending it which render it probable that, even at high velocities, it is less in amount than Mr. Stephenson's estimate.

The position of the eccentrics which is necessary to make the pistons drive the engine forward must be directly the reverse of that which would cause them to drive the engine backwards. To be able, therefore, to reverse the motion of the engine, it would only be necessary to be able to reverse the position of the eccentrics, which may be accomplished by either of two expedients.

_First_, The eccentrics may be capable of revolving on the great working axle, and also of sliding upon it through a small space. Their revolution on the axle may be checked by letting a pin attached to a collar fastened on the axle fall into a hole on the side of the eccentric. Such a pin will drive the eccentric round with the axle, and the position of this pin and the hole will determine the position of the eccentric with reference to the crank. At a short distance [Pg380] on the other side of the eccentric may be a corresponding collar with a pin in the opposite position. By moving the eccentric longitudinally on the axle, the former pin may be withdrawn from the hole, and the latter allowed to fall into the hole on the other side. Proper mechanism may be provided by which the position of the eccentric may thus be reversed in reference to the crank, and by such means the motion of the engine may be reversed.

_Secondly_, Supposing the eccentrics which drive the engine forward to be immovably fixed upon the axle, two other eccentrics may be provided attached to other parts of the same axle, and having a position exactly the reverse with reference to the cranks. Proper mechanism may be provided, by which either or both pairs of eccentrics may be thrown in or out of gear. Such are the means adopted in the engine which has been already described. The eccentrics for driving the engine backwards are placed outside the cranks at F′ F″. A hand lever _w″_ _fig._ 101. is provided, by which the engine man may throw either pair of eccentrics into or out of gear, so as to make the engine work either backwards or forwards.

[Illustration: 108.]

[Illustration: 109.]

[Illustration: 110.]

As all the moving parts of the engine require to be constantly lubricated with oil to diminish the friction, and keep them cool, oil-cups for this purpose are fixed upon them. In some engines these oil-cups are attached separately to all the moving parts: in others they are placed near each other in a row on the boiler, and communicate by small tubes with the several parts required to be lubricated. One of these is requisite for each end of the connecting rods, for each of the guides of the piston-rods, for the piston-rod itself, the spindle of the slide-valve, and other parts. An elevation of one of these oil-cups is shown in _fig._ 108., a vertical section in _fig._ 109., and horizontal plan in _fig._ 110. The cup A is made of brass with a cover B. This cover has a piece projecting from it turning upon a pin in a socket C at the side of the cup A, and square at the end, resting upon a small spring at the bottom of the socket to hold it either open or shut. In the bottom of the [Pg381] cup is inserted an iron tube D extending nearly to the top. This tube projects from the bottom of the cup, where it is tapped for the purpose of fixing the cup on the part of the engine which it is intended to lubricate. The hole into which the cup is screwed communicates with the rubbing surface, and some cotton thread is passed through the tube dipping into the oil in the cup at the one end and touching the moving part at the other. This thread acts as a siphon, and constantly drops oil on the rubbing surface.

[Illustration: _Fig._ 111.]

The tender is a carriage attached behind the engine and close to it, carrying coke for the supply of the furnace, and water for the boiler. The coke is contained in the space R″, (_fig._ 98. 100.) surrounded by a tank I″ containing water to feed the boiler. The feed for the boiler is conducted from the tank through a pipe descending downwards and in a curved direction, P″ Q″, _fig._ 98., and connected with a horizontal pipe K, _fig._ 97. A cock is provided at P″, by which the supply of water to this pipe may be cut off at pleasure. Another cock is provided at _t′_, _fig._ 97., where the curved pipe joins the horizontal pipe by which the quantity of water supplied to K may be regulated by opening the cock more or less fully. The handle of this cock rises through the floor of the engine, so that the engineer may regulate it at discretion. The pipe K being conducted under the engine, as represented in _fig._ 97., terminates in a vertical pipe, of greater diameter, containing two valves, both of which open upwards, and between these valves to this vertical pipe is attached a force-pump, by which the water is drawn from the horizontal pipe K into the vertical pipe K′, and from the latter is driven into a delivery-pipe by which it is forced into the boiler. The details of the interior of this feed-pump are represented on a larger scale in _fig._ 111. The extremity of the horizontal pipe K′ is represented in section at H, where it is joined on by a screw to the bottom of the vertical pipe which is represented in _fig._ 97. at K, and which is here represented in section. The vertical pipe, represented in _fig._ 97. consists of several parts screwed together by nuts and bolts passing through flanges. The lowest piece I is attached by a flange to the piece L: within these is contained the valve Q resting in a seat made conical, so that the ball [Pg382] which forms the valve shall rest in water-tight contact with it. The ball is turned and ground to an accurate sphere, and whatever position it assumes upon its seat its contact will be perfect. It is guided in its upward and downward motion by several vertical bars which confine it, and which are united at the top, so as to limit the upward motion of the ball. A screw V′ is inserted in the bottom of the piece I, by removing which access can be obtained to the valve. The piece L is secured to the short pipe G by nuts and bolts passed through a flange. The pipe G is cast upon the end of the feed-pump A. On the foremost end of this feed-pump is constructed a stuffing-box C of the usual form, having a gland D forced against packing by nuts and screws E. The plunger B is turned so as to be truly cylindrical, and moves in water-tight contact through the gland D. The plunger not being in contact with the inner surface of the pump-barrel A, the latter need not be ground. The horizontal rod by which the plunger B is driven is attached at its foremost extremity to an arm which projects from the rod of the steam-piston, and consequently this plunger is moved through a space equal to the stroke of the steam-piston. In this case that space is eighteen inches. The [Pg383] upper end of the vertical tube G is attached by screws and a flange to a piece P containing a valve R similar in all respects to the lower valve Q, and like it opening upwards. A screw V is introduced at the top by which access may be obtained to this valve. This screw also presses on the crown of the guides of the valve, so as to hold it down by regulated pressure. At the side of this upper piece P is inserted a horizontal tube M connected with the end of the delivery-pipe N. This latter is continued to the boiler with which it communicates at the fire-box. When the plunger B is drawn out of the pump-barrel A, the spherical valve Q being relieved from its downward pressure is raised, and water passes from the pipe H through the valve Q into the vertical pipe G; the lower valve Q then closes and stops the return of the water. The plunger B returning into the pump-barrel A then forces the water against the upper valve R and drives it through the delivery-tube N, from which its return is prevented by the valve R. When the delivery-tube N is filled with water throughout its whole length, every stroke of the plunger will evidently drive into the boiler a volume of water equal to the magnitude of a part of the plunger eighteen inches in length.

Until within the last few years, locomotive engines were supported on only four wheels; they are, however, now almost universally supported on six, the driving wheels being in the middle. To give greater security to the position of the engine between the rails it is usual to construct flanges on the tires of all the six wheels. Mr. Stephenson, however, has been in the practice of constructing the driving wheels without flanges, and with tires truly cylindrical, depending on the flanges of the two pairs of smaller wheels to maintain the engine between the rails. The wheels of the engine here described are constructed in this manner. The driving wheels D′ are fixed on the cranked axle C′, and are five feet in diameter. The other wheels L′ M′, the one being placed immediately behind the smoke-box, and the other immediately behind the fire-box, are each three feet six inches in diameter, and have a flange upon their tires, which running on the [Pg384] inside of each rail keeps the engine between the rails. Each pair of these small wheels, like the driving-wheels, is fixed upon their axle. The axles are 3-5/8 inches diameter, and project beyond the wheels, the projecting part supporting the frame of the engine and turning in brasses. Upon these brasses rest springs, which bear the whole weight of the engine. These springs having nothing between them and the road but the wheels and axles intercept and equalise the sudden shocks produced by the rapid motion upon the road.

When an engine is required for the transport of very heavy loads, such as those of merchandise, the adhesion of one pair of working wheels is found to be insufficient, and, in such cases, one of the two pairs of wheels L′ M′ is made of the same diameter as the wheels which are placed upon the working axle, and a bar is attached to points on the outside of the wheels at equal distances from their centre, connecting them in such a manner that any force applied to make one pair of wheels revolve must necessarily impart the same motion to the other pair. By such means the force of the steam is made to drive both pairs of wheels, and consequently a proportionally increased adhesion is obtained.

The velocity which an engine is capable of imparting to the load which it draws depends upon the rate at which the pistons are capable of being moved in the cylinders. By every motion of each piston backwards and forwards one revolution of the driving wheels is produced, and by each revolution of the driving wheels, supposing them not to slip upon the rails, the load is driven through a distance upon the road equal to their circumference. As the two cylinders work together, it follows, that a quantity of steam sufficient to fill four cylinders supplied by the boiler to the engine will move the train through a distance equal to the circumference of the driving wheels; and in accomplishing this, each piston must move twice from end to end of the cylinder; each cylinder must be twice filled with steam from the boiler; and that steam must be twice discharged from the cylinder through the blast-pipe into the chimney.

[Pg401] If the driving wheels be five feet in diameter their circumference will be fifteen feet seven inches. To drive a train with a velocity of thirty miles an hour, it will be necessary that the engine should be propelled through a space of forty-five feet per second. To accomplish this with five-feet wheels they must be therefore made to revolve at the rate of very nearly three revolutions per second; and as each revolution requires two motions of the piston in the cylinder, it follows that each piston must move three times forwards and three times backwards in the cylinder in a second; that steam must be admitted six times per second from the steam-chest to each cylinder, and discharged six times per second from each cylinder into the blast-pipe. The motion, therefore, of each piston, supposing it to be uniform, must divide a second into six equal parts, and the puffs of the blast-pipe in the chimney must divide a second into twelve equal parts. The motion of the slides and other reciprocating parts of the machinery must consequently correspond.

This motion of the reciprocating parts of the machinery being found to be injurious to it, and to produce very rapid wear, attempts have been made to remedy the defect, and to obtain greater speed with an equal or diminished rate of motion of the piston, by the adoption of driving wheels of greater diameter, and on several of the great lines of railway the magnitude of the wheels for the passenger-engines have been increased to five feet and a half and six feet diameter; but such engines have not been sufficiently long in use to afford grounds for forming a practical estimate of their effects. Experiments of a much bolder description have, however, been tried on one of the great lines of railway by the adoption of driving wheels of much greater diameter. In some cases their magnitude has been increased even to ten feet; but from various experiments to which these engines have been submitted by myself and others, as well as from the experience which appears to be obtained from the results of their ordinary work, it does not appear that any advantages have attended them, and they have been accordingly for the most part abandoned.

The pressure of steam in the boiler is limited by two safety-valves, [Pg402] represented in _fig._ 97. at N and O. The valve at N is under the control of the engineer, but the valve at O is inaccessible to him. The structure of the safety-vale represented at N is exhibited on a larger scale in _fig._ 112., which represents its section, and _fig._ 113., which shows a plan of the valve-seat with the valve removed. The valve A, which is made of brass, is mitred round the edge at an angle of 45°, and has a spindle, or stalk B, cast upon it, projecting downwards from the middle of it. The valve-seat C is also made of brass, and cast with a flange at the bottom to attach it to the boiler. The mitred surface of the valve is ground into the valve-seat, so as to rest in steam-tight contact with it. Across the valve-seat, which is two and a half inches in diameter, is cast a thin piece D, seen in plan in _fig._ 113. and in section in _fig._ 112. which extends from the top to the bottom, and has a longitudinal hole through it, in which the spindle B of the valve works: by this hole it is guided when it rises from its seat. A projection E is cast upon the seat of the valve, in which a standard F is inserted. This standard is forked at the top, and receives the end of a lever G, which turns in it upon a centre. A rod H is jointed to this lever by another pin at three inches from the former, and the lower end of this rod, ground to a point, presses upon the centre of the valve A. At the other end of the lever, which is broken off in _fig._ 112., at a distance of three feet from the centre pin, inserted in the fork of the pillar F, the rod of a common spring-balance _w_, _fig._ 101., is attached by a finger-nut _n_. The bottom of this spring-balance is secured on to the fire-box. This balance is screwed up by the finger-nut on the valve-lever until the required pressure on the lever is produced through the medium of the rod H, this pressure being generally fifty pounds per square inch above the atmosphere. When the pressure of the steam in the boiler exceeds this, the valve A is raised from its seat, and the steam escapes.

[Illustration: _Fig._ 112.]

[Illustration: _Fig._ 113.]

It is evident that the sliding weight by which the pressure [Pg403] of the safety-valve is sometimes regulated in stationary engines would not be admissible in a locomotive engine, since the motion of the engine would constantly jolt it up and down, and cause the steam to escape. One of the disadvantages attending the use of the spring-valve is that it cannot be opened to let the steam escape without increasing its force, so that the steam, when escaping, must really have a greater pressure than that to which the valve has been previously adjusted. The longer the lever is, the greater will be this difference of pressure, inasmuch as a given elevation of the pin governing the rod H would cause a proportionally greater motion in that end of the lever attached to the spring.

The second safety-valve O is enclosed in a case, so that it is inaccessible, and its purpose is to limit the power of the engineer to increase the pressure of steam in the boiler. This valve is similar in construction to the former, but instead of being held down by a lever, is pressed upon by several small elliptical springs placed one above another over the valve, and held down by a screw which turns in a frame Y, fixed into the valve-seat. By this screw the pressure on the valve can be adjusted to any required degree; and if the open safety-valve be screwed down to a greater pressure, the steam will begin to escape from this second valve.

Also in the case where the boiler produces surplus steam faster than its escape can be effected at the valve N, the pressure will sometimes be increased until the valve O is opened, and its escape will take place from both valves.

The whole weight of the engine bears upon those parts of the six axles R′, _fig._ 99., which project beyond the wheels. Boxes are formed in which these parts of the axles turn, and through the medium of which the weight of the engine rests upon them. Over these boxes are constructed oil or grease cups, by means of which the axles are constantly lubricated. It is usual to lubricate the axles of the engine itself with oil: the axles of the tender, and other coaches and waggons, are lubricated with a mixture of oil and tallow. In the middle of the box in which the axle turns, and between the two oil-cups, is cast a socket, in which the end of the spindle on [Pg404] which the spring presses rests. The springs are composed of a number of steel-plates, laid, in the usual manner, one above the other, increasing in length upwards. In the engine here described, the plates forming the springs of the driving wheels are thirteen in number, each of which is four inches in width, and 5/16ths of an inch in thickness. The springs upon the other wheels are three inches in width. The springs of the driving wheels are below the axle, while those of the smaller wheels are above it.

Buffers D″ are placed behind the tender, which act upon a spring C (_fig._ 100.), to break the collision, when the waggons or carriages strike upon the tender, and similar buffers are attached to all passenger-coaches. Some of these buffers are constructed with a system of springs similar to C, but more elastic, and combined in greater number under the framing of the carriage, so that a considerable play is allowed to them. In some cases the rods of the buffers are made to act upon strong spiral springs inserted in the sides of the framing of the carriage. This arrangement gives greater play to the buffers; and as every coach in a train has several buffers, the combined effect of these is such, that a considerable shock given to either end of the train may be rendered harmless by being spent upon the elasticity of these several systems of springs.

In order to give notice of the approach of a train, a steam-whistle Z′, _fig._ 97. 101., is placed immediately above the fire-box at the back of the engine. This is an apparatus composed of two small hemispheres of brass, separated one from the other by a small space. Steam is made to pass through a hollow space constructed in the lower hemisphere, and escapes from a very narrow circular opening round the edge of that hemisphere, rushing up with a force proportionate to its pressure. The edge of the upper hemisphere presented downwards encounters this steam, and an effect is produced similar to the action of air in organ pipes. A shrill whistle is produced, which can be heard at a very considerable distance, and, differing from all ordinary sounds, it never fails to give timely notice of the approach of a train.

The water tank I″, _fig._ 98. 100., which is constructed on the tender, is formed of wrought-iron plates 1/8 of an inch thick, [Pg405] riveted at the corners by angle iron already described. This tank is 9 feet long, 6-3/4 feet wide, and 2-1/4 feet deep. The top is covered with a board K″, and a raised platform N″ is constructed behind, divided into three parts, covered with leads, which open on hinges. The middle lid covers an opening to the tank by which water is let in: the lids at either side cover boxes in which are contained the tools necessary to be carried with the engine. The curved pipe P″, _fig._ 98., leading from the bottom of the tank to the pipe Q″, is of copper. The pipe Q″, connecting the latter with the feed-pipe K′, _fig._ 99., is sometimes formed of leather or India-rubber cloth, having a spiral spring on the inside to prevent it from collapsing. It is necessary that this pipe Q″ should have a power of yielding to a sufficient degree to accommodate itself to the inequalities of motion between the engine and tender. A metal pipe is sometimes used, supplied with a double ball and socket, and a telescopic joint, having sufficient play to allow for the lateral and longitudinal inequalities of motion of the engine and tender. The weight of an engine, such as that here described, supplied with its proper quantity of water and fuel, is about 12 tons: the tender, when empty, weighs about 3-1/4 tons; and when filled with water and fuel its weight is 7 tons. The tank contains 700 gallons of water, and the tender is capable of carrying about 800 weight of coke. This supply is sufficient for a trip of from thirty to forty miles with an ordinary load.

(198.) It is not usual to express the power of locomotive engines in the same manner as that of other engines by the term horse-power. Indeed, until the actual amount of resistance opposed to these machines, under the various circumstances in which they are worked, shall be ascertained with some degree of precision, it is impossible that their power or efficiency can be estimated with any tolerable degree of approximation. The quantity of water evaporated, and passed in steam through the cylinders, supplies a major limit to the power exerted; but even this necessary element for the calculation of the efficacy of these machines has not been ascertained by a sufficiently extensive course of observation and experiment. Mr. Stephenson states, that the engine which [Pg406] has been here described is capable of evaporating 77 cubic feet of water per hour, while the early locomotives could only evaporate 16 cubic feet per hour. This evaporation, however, is inferior to that which I have ascertained myself to be produced by engines in regular operation on some of the northern railways. In an experiment made in July, 1839, with the Hecla engine, I found that the evaporation in a trip of ninety-five miles, from Liverpool to Birmingham, was at the rate of 93·2 cubic feet per hour, and in returning the same distance it was at the rate of 85·7 cubic feet per hour, giving a mean of 89 cubic feet per hour nearly. The Hecla weighed 12 tons; and its dimensions and proportions corresponded very nearly with those of the engine above described.

In a course of experiments which I made upon the engines then in use on the Grand Junction Railway in the autumn of 1838 I found that the ordinary evaporating power of these engines varied from eighty to eighty-five cubic feet per hour.

Engines of much greater dimensions, and consequently of greater evaporating power, are used on the Great Western Railway. In the autumn of 1838 experiments were made upon these engines by Mr. Nicholas Wood and myself, when we found that the most powerful engine on that line, the North Star, drawing a load of 110-1/2 tons gross, engine and tender inclusive, at 30-1/2 miles an hour, evaporated 200 cubic feet of water per hour. The same engine drawing a load of 194-1/2 tons at 18-1/2 miles an hour evaporated 141 cubic feet per hour, and when drawing 45 tons at 38-1/2 miles an hour evaporated 198 cubic feet of water per hour.

It has been already shown that a cubic foot of water evaporated per hour produces a gross amount of mechanical force very little less than two-horse power, and consequently the gross amount of mechanical power evolved in these cases by the evaporation of the locomotive boilers will be very nearly twice as many horse-power as there are cubic feet of water evaporated per hour. Thus the evaporation of the Hecla, in the experiments made in July, 1839, gave a gross power of about one hundred and eighty horses, while the evaporation of the North Star gave a power of about four hundred horses. In stationary engines about half the gross [Pg407] power evolved in the evaporation is allowed for waste, friction, and other sources of resistance not connected with the load. What quantity should be allowed for this in locomotive engines is not yet ascertained, and therefore it is impossible to state what proportion of the whole evaporation is to be taken as representing the useful horse-power.

(199.) The great uniformity of resistance produced by the traction of carriages upon a railway is such as to render the application of steam power to that purpose extremely advantageous. So far as this resistance depends on mechanical defects, it is probably rendered as uniform as is practicable, and in proportion to the quantity of load carried is reduced to as small an amount as it is likely to attain under any practicable circumstances. Until a recent period this resistance was ascribed altogether, or nearly so, to mechanical causes. The inequalities of the road-surface, the friction of the axles of the wheels in their bearings, and the various sources of resistance due to the machinery of the engine, being the principal of these resistances, were for the most part independent of the speed with which the train was moved; and it was accordingly assumed in all calculations respecting the power of locomotive engines that the resistance would be practically the same whatever might be the speed of the train. It had been well understood that so far as the atmosphere might offer resistance to the moving power this would be dependent on the speed, and would increase in a very high ratio with the speed; but it was considered that the part of the resistance due to this cause formed a fraction of the whole amount so insignificant that it might be fairly disregarded in practice, or considered as a part of the actual computed resistance taken at an average speed.

It has been, until a late period, accordingly assumed that the total amount of resistance to railway trains which the locomotive engines have had to overcome was about the two hundred and fiftieth part of the gross weight of the load drawn: some engineers estimated it at a two hundred and twentieth; others at a two hundred and fiftieth; others at a three hundred and thirtieth part of the load; and the two hundred and fiftieth part of the gross load drawn may perhaps be [Pg408] considered as a mean between these much varying estimates. What the experiments were, if any, on which these rough estimates were based, has never appeared. Each engineer formed his own valuation of this effect, but none produced the experimental grounds of their opinion. It has been said that the trains run down the engine, or that the drawing chains connecting the engine slacken in descending an inclination of sixteen feet in a mile, or 1/330. Numerous experiments, however, made by myself, as well as the constant experience now daily obtained on railways, show that this is a fallacious opinion, except at velocities so low as are never practised on railways.

(200.) In the autumn of 1838 a course of experiments was commenced at the suggestion of some of the proprietors of the Great Western Railway Company, with a view to determine various points connected with the structure and the working of railways. A part of these experiments were intended to determine the mean amount of the resisting force opposed to the moving power, and this part was conducted by me. After having tried various expedients for determining the mean amount of resistance to the moving power, I found that no method gave satisfactory results except one founded on observing the motion of trains by gravity down steep inclined planes. When a train of waggons or coaches is placed upon an inclined plane so steep that it shall descend by its gravity without any moving power, its motion, when it proceeds from a state of rest, will be gradually accelerated, and if the resistance to that motion was, as it has been commonly supposed to be, uniform and independent of the speed, the descent would be uniformly accelerated: in other words, the increase of speed would be proportional to the time of the motion. Whatever velocity the train would gain in the first minute, it would acquire twice that velocity at the end of the second minute, three times that velocity at the end of the third minute, and so on; and this increase of velocity would continue to follow the same law, however extended the plane might be. That such would be the law which the descending motion of a train would follow had always been supposed, up to the time of the experiments now referred to; and it was even maintained by some that [Pg409] such a law was in strict conformity with experiments made upon railways and duly reported. The first experiments instituted by me at the time just referred to afforded a complete refutation of this doctrine. It was found that the acceleration was not uniform, but that with every increase of speed the acceleration was lessened. Thus if a certain speed were gained by a train in one second when moving at five miles an hour, a much less speed was gained in one second when moving ten miles an hour, and a comparatively small speed was gained in the same time when moving at fifteen miles an hour, and so on. In fact, the augmentation of the rate of acceleration appeared to diminish in a very rapid proportion as the speed increased: this suggested to me the probability that a sufficiently great increase of speed would destroy all acceleration, and that the train would at length move at a uniform velocity. In effect, since the moving power which impels a train down an inclined plane of uniform inclination is that fraction of the gross weight of the train which acts in the direction of the plane, this moving power must be necessarily invariable; and as any acceleration which is produced must arise from the excess of this moving power over the resistance opposed to the motion of the train, from whatever causes that resistance may arise, whenever acceleration ceases, the moving force must necessarily be equal to the resistance; and therefore, when a train descends an inclined plane with a uniform velocity, the gross resistance to the motion of the train must be equal to the gross weight of the train resolved in the direction of the plane; or, in other words, it must be equal to that fraction of the whole weight of the train which is expressed by the inclination of the plane. Thus if it be supposed that the plane falls at the rate of one foot in one hundred, then the force impelling the train downwards will be equal to the hundredth part of the weight of the train. So long as the resistance to the motion of the train continues to be less than the hundredth part of its weight, so long will the motion of the train be accelerated; and the more the hundredth part of the weight exceeds the resistance, the more rapid will the acceleration be; and the less the hundredth part of the weight [Pg410] exceeds the resistance, the less rapid will the acceleration be. If it be true that the amount of resistance increases with the increase of speed, then a speed may at length be attained so great that the amount of resistance to the motion of the train will be equal to the hundredth part of the weight. When that happens, the moving power of a hundredth part of the weight of the train being exactly equal to the resistance to the motion, there is no excess of power to produce acceleration, and therefore the motion of the train will be uniform.

Founded on these principles, a vast number of experiments were made on planes of different inclinations, and with loads of various magnitudes; and it was found, in general, that when a train descended an inclined plane, the rate of acceleration gradually diminished, and at length became uniform; that the uniform speed thus attained depended on the weight, form, and magnitude of the train and the inclination of the plane; that the same train on different inclined planes attained different uniform speeds—on the steeper planes a greater speed being attained. From such experiments it followed, contrary to all that had been previously supposed, that the amount of resistance to railway trains had a dependence on the speed; that this dependence was of great practical importance, the resistance being subject to very considerable variation at different speeds, and that this source of resistance arises from the atmosphere which the train encounters. This was rendered obvious by the different amount of resistance to the motion of a train of coaches and to that of a train of low waggons of equal weight.

The former editions of this work having been published before the discovery which has resulted from these experiments, the average amount of resistance to railway trains, there stated, and the conclusions deduced therefrom, were in conformity with what was then known. It was stated that the resistance to the moving power was practically independent of the speed, and on level rails was at the average rate of about seven pounds and a half per ton. This amount would be equivalent to the gravitation of a load down an inclined plane falling 1/300, and consequently in ascending such a plane the moving power would have to encounter twice [Pg411] the resistance opposed to it on a level. As it was generally assumed that a locomotive-engine could not advantageously vary its tractive power beyond this limit, it was therefore inferred that gradients (as inclinations are called) ought not to be constructed of greater steepness than 1/300. It was supposed that in descending gradients more steep than this the train would be accelerated and would require the use of the brake to check its motion, while in ascending such planes the engine would be required to exert more than twice the ordinary tractive power required on level rails. As the resistance produced by the air was not taken into consideration, no distinction was made between heavy trains of goods presenting a frontage and magnitude bearing a small proportion to their gross weight and lighter trains of passenger-coaches presenting great frontage and great magnitude in proportion to their weight. The result of the experiments above explained leads to inferences altogether at variance with those which have been given in former editions of the present work, and which were then universally admitted by railway engineers. The tendency of the results of these experiments show that low gradients on railways are not attended with the advantageous effects which have been hitherto ascribed to them; that, on the contrary, the resistance produced by steeper gradients can be compensated by slackening the speed, so that the power shall be relieved from as much atmospheric resistance by the diminution of velocity as is equal to the increased resistance produced by the gravity of the plane which is ascended. And, on the other hand, in descending the plane the speed may be increased until the resistance produced by the atmosphere is increased to the same amount as that by which the train is relieved of resistance by the declivity down which it moves. Thus, on gradients, the inclination of which is confined within practical limits, the resistance to the moving-power may be preserved uniform, or nearly so, by varying the velocity.

(201.) The series of experiments which have established these general conclusions have not yet been sufficiently extended and varied to supply a correct practical estimate of the limit which it would be most advantageous to impose upon the [Pg412] gradients of railways; but it is certain that railways may be laid down, without practical disadvantage, with gradients considerably steeper than those to which it has been hitherto the practice to recommend as a limit.

The principle of compensation by varied speed being admitted, it will follow that the time of transit between terminus and terminus of a line of railway laid down with gradients, varying from twenty to thirty feet a mile, will be practically the same as it would be on a line of the same length constructed upon a dead level; and not only will the time of transport be equal, but the quantity of moving power expended will not be materially different. The difference between the circumstances of the transport in the two cases will be merely that, on the undulating line, a varying velocity will be imparted to the train and a varying resistance opposed to the moving power; while on the level line the train would be moved at a uniform speed, and the engine worked against a uniform resistance. These conclusions have been abundantly confirmed by the experiments made in last July with the Hecla engine above referred to. The line of railway between Liverpool and Birmingham on which the experiment was made extended over a distance of ninety-five miles, and the gradients on which the effects were observed varied from a level to thirty feet per mile, a great portion of the line being a dead level. The following table shows the uniform speed with which the train ascended and descended the several gradients, and also the mean of the ascent and descent in each case, as well as the speed upon the level parts of the line:—

—————————————————————————————————————————————————— | Speed. | |———————————————-———————————————————————— Gradient.| Ascending. | Descending. | Mean. —————————————————————————————————————————————————— One in |Miles per hour.|Miles per hour.| 177 | 22·25 | 41·32 | 31·78 265 | 24·87 | 39·13 | 32·00 330 | 25·26 | 37·07 | 31·16 400 | 26·87 | 36·75 | 31·81 532 | 27·35 | 34·30 | 30·82 590 | 27·37 | 33·16 | 30·21 650 | 29·03 | 32·58 | 30·80 | | |———————— Level | | | 30·93 ——————————————————————————————————————————————————

[Pg413] From this table it is apparent that the gradients do possess the compensating power with respect to speed already mentioned. The discrepancies existing among the mean values of the speed are only what may be fairly ascribed to casual variations in the moving power. The experiment was made under favourable circumstances: little disturbance was produced from the atmosphere; the day was quite calm. In the same experiment it was found that the water evaporated varied very nearly in proportion to the varying resistance, and the amount of that evaporation may be taken as affording an approximation to the mean amount of resistance. Taking the trip to and from Birmingham over the distance of 190 miles, the mean evaporation per mile was 3·36 cubic feet of water. The volume of steam produced by this quantity of water will be determined approximately by calculating the number of revolutions of the driving wheels necessary to move the engine one mile. The driving wheels being 5 feet in diameter, their circumference was 15·7 feet, and consequently in passing over a mile they would have revolved 336·3 times. Since each revolution consumes four cylinders full of steam, the quantity of steam supplied by the boiler to the cylinders per mile will be found by multiplying the contents of the cylinder by four times 336·3, or 1345·2.

The cylinders of the Hecla were 12-1/2 inches diameter, and 18 inches in length, and consequently their contents were 1·28 cubic feet for each cylinder: this being multiplied by 1345·2 gives 1721·86 or 1722 cubic feet of steam per mile. It appears, therefore, that supposing the priming either nothing or insignificant, which was considered to be the case in these experiments, 3·36 cubic feet of water produced 1722 cubic feet of steam, of the density worked in the cylinders. The ratio, therefore, of the volume of this steam to that of the water producing it, was 1722 to 3·36, or 512·5 to 1. The pressure of steam of this density would be 54·5 pounds per square inch.[34] Such, therefore, was the limit of the average total pressure of the steam in the cylinders. In this experiment the safety-valve of the boiler was screwed down to 60 pounds per square [Pg414] inch above the atmospheric pressure, which was therefore the major limit of the pressure of steam in the boiler; but as the actual pressure in the boiler must have been less than this amount, the difference between the pressure in the cylinder and boiler could not be ascertained. This difference, however, would produce no effect on the moving power of the steam, since the pressure of steam in the cylinders obtained by the above calculation is quite independent of the pressure in the boiler, or of any source of error except what might arise from priming. The pressure of 54·5 pounds per square inch, calculated above, being the total pressure of the steam on the pistons, let 14·5 pounds be deducted from it, to represent the atmospheric pressure against which the piston must act, and the remaining 40 pounds per square inch will represent the whole available force drawing the train and overcoming all the resistances arising from the machinery of the engine, including that of the blast-pipe. The magnitude of a 12-1/2 inch piston being 122·7 square inches, the total area of the two pistons would be 245·2 square inches, and the pressure upon each of 40 pounds per inch would give a total force of 9816 on the two pistons. Since this force must act through a space of three feet, while the train is impelled through a space of 15·7 feet, it must be reduced in the proportion of 3 to 15·7, to obtain its effect at the point of contact of the wheels upon the rails: this will give 1875 pounds as the total force exerted in the direction of the motion of the train. The gross weight of the train being 80 tons, including the engine and tender, this would give a gross moving force along the road of about 23·4 pounds per ton of the gross load, this force being understood to include all the resistances due to the engine. This resistance corresponds to the gravitation of a plane rising at the rate of 1/95, and therefore it appears that such would be the inclination of the plane by the gravitation of which the gross resistance would be doubled, instead of such inclination being about 1/300, as has been hitherto supposed.

Since the remarkable and unexpected results of this series of experiments became known various circumstances were brought to light, which were before unnoticed, and which [Pg415] abundantly confirm them. Among these may be mentioned the fact, that in descending the Madeley plane, on the Grand Junction Railway, which falls for above three miles at the rate of twenty-nine feet a mile, the steam can never be entirely cut off. But, on the other hand, to maintain the necessary speed in descending, the power of the engine is always necessary. As this plane greatly exceeds that which would be sufficient to cause the free motion of the train down it, the power of the engine expended in descending it, besides all that part of the gravitating power of the plane which exceeds the resistance due to friction and other mechanical causes must be worked against the atmosphere.

This estimate of the resistance is also in conformity with the results of a variety of experiments made by me with trains of different magnitudes down inclined planes of various inclinations.

(202.) In laying out a line of railway the disposition of the gradients should be such as to preserve among them as uniform a character as is practicable, for the weight and power of the engine must necessarily be regulated by the general steepness of the gradients. Thus if upon a railway which is generally level, like that between Liverpool and Manchester, one or two inclined planes of a very steep character occur, as happens upon that line, then the engine which is constructed to work upon the general gradients of the road is unfit to draw the same load up those inclinations which form an exception to the general character of the gradients. In such cases some extraordinary means must generally be provided for surmounting those exceptionable inclinations. Several expedients have been proposed for this purpose, among which the following may be mentioned:—

1. Upon arriving at the foot of the plane the load is divided, and the engine carries it up in several successive trips, descending the plane unloaded after each trip. The objection to this method is the delay which it occasions—a circumstance which is incompatible with a large transport of passengers. From what has been stated, it would be necessary, when the engine is fully loaded on a level, to divide its load into two or more parts, to be successively [Pg416] carried up when the incline rises 52 feet per mile. This method has been practised in the transport of merchandise occasionally, when heavy loads were carried on the Liverpool and Manchester line, upon the Rainhill incline.

2. A subsidiary or assistant locomotive engine may be kept in constant readiness at the foot of each incline, for the purpose of aiding the different trains, as they arrive, in ascending. The objection to this method is the cost of keeping such an engine with its boiler continually prepared, and its steam up. It is necessary to keep its fire continually lighted, whether employed or not; otherwise, when the train would arrive at the foot of the incline, it should wait until the subsidiary engine was prepared for work. In cases where trains would start and arrive at stated times, this objection, however, would have less force. This method is at present generally adopted on the Liverpool and Manchester line.

3. A fixed steam-engine may be erected on the crest of the incline, so as to communicate by ropes with the train at the foot. Such an engine would be capable of drawing up one or two trains together, with their locomotives, according as they would arrive, and no delay need be occasioned. This method requires that the fixed engine should be kept constantly prepared for work, and the steam continually up in the boiler.

4. In working on the level, the communication between the boiler and the cylinder in the locomotives may be so restrained by

## partially closing the throttle-valve, as to cause the pressure

upon the piston to be less in a considerable degree than the pressure of steam in the boiler. If under such circumstances a sufficient pressure upon the piston can be obtained to draw the load on the level, the throttle-valve may be opened on approaching the inclined plane, so as to throw on the piston a pressure increased in the same proportion as the previous pressure in the boiler was greater than that upon the piston. If the fire be sufficiently active to keep up the supply of steam in this manner during the ascent, and if the rise be not greater in proportion than the power thus obtained, the locomotive will draw the load up the incline without further assistance. It is, however, to be observed, that in this case [Pg417] the load upon the engine must be less than the amount which the adhesion of its working wheels with the railroad is capable of drawing; for this adhesion must be adequate to the traction of the same load up the incline, otherwise, whatever increase of power might be obtained by opening the throttle-valve, the drawing wheels would revolve without causing the load to advance. This method has been generally practised upon the Liverpool and Manchester line in the transport of passengers; and, indeed, it is the only method yet discovered which is consistent with the expedition necessary for that species of traffic.

In the practice of this method considerable aid may be derived also by suspending the supply of feeding water to the boiler during the ascent. It will be recollected that a reservoir of cold water is placed in the tender which follows the engine, and that the water is driven from this reservoir into the boiler by a forcing pump, which is worked by the engine itself. This pump is so constructed that it will supply as much cold water as is equal to the evaporation, so as to maintain constantly the same quantity of water in the boiler. But it is evident, on the other hand, that the supply of this water has a tendency to check the rate of evaporation, since in being raised to the temperature of the water with which it mixes it must absorb a considerable portion of the heat supplied by the fire. With a view to accelerate the production of steam, therefore, in ascending the inclines, the engine man may suspend the action of the forcing pump, and thereby stop the supply of cold water to the boiler; the evaporation will go on with increased rapidity, and the exhaustion of water produced by it will be repaid by the forcing pump on the next level, or still more effectually on the next descending incline. Indeed the feeding pump may be made to act in descending an incline, if necessary, when the action of the engine itself is suspended, and when the train descends by its own gravity, in which case it will perform the part of a brake upon the descending train.

5. The mechanical connexion between the piston of the cylinder and the points of contact of the working wheels with the road may be so altered, upon arriving at the incline, as to [Pg418] give the piston a greater power over the working wheels. This may be done in an infinite variety of ways, but hitherto no method has been suggested sufficiently simple to be applicable in practice; and even were any means suggested which would accomplish this, unless the intensity of the impelling power were at the same time increased, it would necessarily follow that the speed of the motion would be diminished in exactly the same proportion as the power of the piston over the working wheels would be increased. Thus, on the inclined plane, which rises fifty-five feet per mile, upon the Liverpool line, the speed would be diminished to nearly one fourth of its amount upon the level.

[Illustration]

FOOTNOTES:

[30] Some of the preceding observations on inland transport, as well as other parts of the present chapter, appeared in articles written by me in the _Edinburgh Review_ for October, 1832, and October, 1834.

[31] Wood on Railroads, 2d edit.

[32] The cost of coke has risen considerably since the date of this report.

[33] I am indebted to the enlarged edition of Tredgold on the Steam Engine, published by Mr. Weale, for the drawings of this engine. The details of the machine are very fully given in that work, the description of them being supplied by Mr. Stephenson himself.

[34] See Table of Pressures, Temperatures, and Volumes, in appendix.

[Pg419]

[Illustration]

CHAP. XII.

LOCOMOTIVE ENGINES ON TURNPIKE ROADS.

RAILWAYS AND STONE ROADS COMPARED. — MR. GURNEY'S STEAM ENGINE. — CONVENIENCE AND SAFETY OF STEAM CARRIAGES. — HANCOCK'S STEAM ENGINE. — OGLE'S STEAM ENGINE. — TREVETHICK'S INVENTION. — DR. CHURCH'S STEAM ENGINE.

(203.) We have hitherto confined our observations on steam-power, as a means of transport by land, to its application on railways. But modern speculation has not stopped there; various attempts have been made, and attended with more or less success, to work steam-carriages on common roads. The mere practicability of this project had long been regarded as very questionable; but enough has been done to show that the only doubt which can attend it, is as to whether it can be profitably resorted to, as a means of transport, and this question [Pg420] has been materially affected by the recent extension of railways. In comparing the effect of a stone road with an iron railway, there are two circumstances which give great superiority and advantage to the latter: first, the resistance opposed by a railway to the moving power, no matter what that moving power may be, is considerably less in proportion to the load than on a stone road. The average resistance on a good level stone road, to the motion of carriages drawn at the speed usually attained by the application of horse-power, may be taken at about a thirty-sixth part of the load, while the resistance to a load drawn upon a railway _at the same speed_ probably does not amount to a tenth part of this resistance. Thus the moving power, whatever it may be, would produce on a railway ten times the useful effect which it would produce on a stone road; secondly, the resistance which is opposed to the moving power on a level railway is much more uniform than on a stone road, and, consequently, the moving power is less subjected to jerks and inequalities. This renders the application of inanimate power more easy on the railway. Those inequalities of surface which increase the amount of resistance on stone roads as compared with railways also produce a jolting motion in the carriage, to counteract which, the use of springs become necessary. These springs render the motion of that part of the carriage which rests upon them different from that part of the carriage which supports them; and in the application of steam-machinery it becomes necessary so to connect the moving power with the wheels that the machinery may have one motion, and the wheels which are put in mechanical connexion with that machinery, and driven by it, shall have another motion. This, it is true, is the case with locomotive engines on railways; but owing to the greater smoothness and equality of the railway surface the difference between the motion of the carriage body suspended on springs and that of the wheels is much less than it would be on a stone road.

But besides the greater smoothness of railways compared with stone roads, the latter have another disadvantage, the effects of which have probably been exaggerated by those who are opposed to this application of steam-power. One of the [Pg421] laws of adhesion long since developed by experiment, and established as a principle of practical science, is that the adhesion is greater between surfaces of the same than between surfaces of a different kind. Thus between two metals of the same kind, the adhesion corresponding to any given pressure is greater than between two metals of different kinds; between two metals of any sort the adhesion is greater than between metal and stone, or between metal and wood. Hence, the wheels of steam-carriages running on a railroad have a greater adhesion with the road, and therefore offer a greater resistance to slip round without the advance of the carriage, than wheels would offer on a turnpike road; for on a railroad the iron tire of the wheel rests in contact with the iron rail, while on a common road the iron tire rests in contact with the surface of stone, or whatever material the road may be composed of. Besides this, the dust and loose matter which necessarily collect on a common road, when pressed between the wheels and the solid base of the road, act somewhat in the manner of rollers, and give the wheels a greater facility to slip than if the road were swept clean, and the wheels rested in immediate contact with its hard surface. The truth of this observation is illustrated on the railroads themselves, where the adhesion is found to be diminished whenever the rails are covered with any extraneous matter, such as dust or moist clay. Although the adhesion of the wheels of a carriage with a common road, however, be less than those of the wheels of a steam-carriage with a railroad, yet still the actual adhesion on turnpike roads is greater in amount than has been generally supposed, and is quite sufficient to propel carriages drawing after them loads of large amount.

The relative facility with which carriages are propelled on railroads and turnpike-roads equally affects any moving power, whether that of horses or steam engines; and whether loads be propelled by the one power or the other, the railroad, as compared with the turnpike-road, will always possess the same proportionate advantage; and a given amount of power, whether of the one kind or the other, will always perform a quantity of work less in the same proportion on a [Pg422] turnpike-road than on a rail-road. But, on the other hand, the expense of original construction, and of maintaining the repairs of a rail-road, is to be placed against the certain facility which it offers to draught.

In the attempts which have been made to adapt locomotive engines to turnpike-roads, the projectors have aimed at the accomplishment of two objects: first, the construction of lighter and smaller engines; and, secondly, increased power. These ends, it is plain, can only be attained, with our present knowledge, by the production of steam of very high temperature and pressure, so that the smallest volume of steam shall produce the greatest possible mechanical effect. The methods of propelling the carriage have been in general similar to that used in the railroad engines, viz. either by cranks placed on the axles, the wheels being fixed upon the same axles, or by connecting the piston rods with the spokes of the wheels. In some carriages, the boiler and moving power, and the body of the carriage which bears the passengers, are placed on the same wheels. In others, the engine is placed on a separate carriage, and draws after it the carriage which transports the passengers, as is always the case on railways.

The chief difference between the steam engines used on railways, and those adapted to propel carriages on turnpike roads, is in the structure of the boiler. In the latter it is essential that, while the power remains undiminished, the boiler should be lighter and smaller. The accomplishment of this has been attempted by various contrivances for so distributing the water as to expose a considerable quantity of surface in contact with it to the action of the fire: spreading it in thin layers on flat plates; inserting it between plates of iron placed at a small distance asunder, the fire being admitted between the intermediate plates; dividing it into small tubes, round which the fire has play; introducing it between the surfaces of cylinders placed one within another, the fire being admitted between the alternate cylinders,—have all been resorted to by different projectors.

(204.) First and most prominent in the history of the application of steam to the propelling of carriages on turnpike roads stands the name of Mr. Goldsworthy Gurney, a medical [Pg423] gentleman, and scientific chemist, of Cornwall. In 1822, Mr. Gurney succeeded Dr. Thompson as lecturer on chemistry at the Surrey Institution; and, in consequence of the results of some experiments on heat, his attention was directed to the project of working steam-carriages on common roads; and he subsequently devoted his exertions in perfecting a steam-engine capable of attaining the end he had in view.

The mistake which so long prevailed in the application of locomotives on railroads, and which, as we have shown, materially retarded the progress of that invention, was shared by Mr. Gurney. Without reducing the question to the test of experiment, he took for granted, in his first attempts, that the adhesion of the wheels with the road was too slight to propel the carriage. He was assured, he says, by eminent engineers, that this was a point settled by actual experiment. It is strange, however, that a person of his quickness and sagacity did not inquire after the particulars of these "actual experiments." So, however, it was; and, taking for granted the inability of the wheels to propel, he wasted much labour and skill in the contrivance of levers and propellers, which acted on the ground in a manner somewhat resembling the feet of horses, to drive the carriage forward. After various fruitless attempts of this kind, the experience acquired in the trials to which they gave rise at last forced the truth upon his notice, and he found that the adhesion of the wheels was not only sufficient to propel the carriage heavily laden on level roads, but was capable of causing it to ascend all the hills which occur on ordinary turnpike-roads. In this manner it ascended all the hills between London and Barnet, London and Stanmore, Stanmore Hill, Brockley Hill, and mounted Old Highgate Hill, the last at one point rising one foot in nine.

[Illustration: _Fig._ 114.]

[Illustration: _Fig._ 115.]

The boiler of Mr. Gurney's engine is so constructed, that there is no part of it in which metal exposed to the action of the fire is out of contact with water. If it be considered how rapidly the

## action of an intense furnace destroys metal when water is not

present to prevent the heat from accumulating, the advantage of this circumstance will be appreciated. In the boiler of Mr. Gurney, the grate-bars [Pg424] themselves are tubes filled with water, and form, in fact, a part of the boiler itself. This boiler consists of three strong metal cylinders placed in a horizontal position one above the other. A section, made by a perpendicular or vertical plane, is represented in _fig._ 114. The ends of the three cylinders just mentioned are represented at D, H, and I. In the side of the lowest cylinder D are inserted a row of tubes, a ground plan of which is represented in _fig._ 115. These tubes, proceeding from the side of the lowest cylinder D, are inclined [Pg425] slightly upwards, for a reason which I shall presently explain. From the nature of the section, only one of these tubes is visible in _fig._ 114. at C. The other extremities of these tubes at A are connected with the same number of upright tubes, one of which is shown at E. The upper extremities G of these upright tubes are connected with another set of tubes K, equal in number, proceeding from G, inclining slightly upwards, and terminating in the second cylinder H.

[Illustration: _Fig._ 116.]

An end view of the boiler is exhibited in _fig._ 116., where the three cylinders are expressed by the same letters. Between the cylinders D and H there are two tubes of communication B, and two similar tubes between the cylinders H and I. From the nature of the section these appear only as a single tube in _fig._ 114. From the top of the cylinder I proceeds a tube N, by which steam is conducted to the engine.

It will be perceived that the space F is enclosed on every side by a grating of tubes, which have free communication with the cylinders D and H, which cylinders have also a free communication with each other by the tubes B. It follows, [Pg426] therefore, that if water be supplied to the cylinder I, it will descend through the tubes, and first filling the cylinder D and the tubes C, will gradually rise in the tubes B and E, will next fill the tubes K and the cylinder H. The grating of water-pipes C E K forms the furnace, the pipes C being the fire-bars, and the pipes E and K being the back and roof of the stove. The fire-door, for the supply of fuel, appears at M, fig. 116. The flue issuing between the tubes F is conducted over the tubes K, and the flame and hot air are carried off through a chimney. That portion of the heat of the burning fuel, which in other furnaces destroys the bars of the grate, is here expended in heating the water contained in the tubes C. The radiant heat of the fire acts upon the tubes K, forming the roof of the furnace, on the tube E at the back of it, and partially on the cylinders D and H, and the tubes B. The draft of hot air and flame passing into the flue at A acts upon the posterior surfaces of the tubes E, and the upper sides of the tubes K, and finally passes into the chimney.

As the water in the tubes C E K is heated, it becomes specifically lighter than water of a less temperature, and consequently acquires a tendency to ascend. It passes, therefore, rapidly into H. Meanwhile the colder portions descend, and the inclined positions of the tubes C and K give play to this tendency of the heated water, so that a prodigiously rapid circulation is produced, when the fire begins to act upon the tubes. When the water acquires such a temperature that steam is rapidly produced, steam-bubbles are constantly formed in the tubes surrounding the fire; and if these remained stationary in the tubes, the action of the fire would not only decompose the steam, but render the tubes red hot, the water not passing through them to carry off the heat. But the inclined position of the tubes, already noticed, effectually prevents this injurious consequence. A steam-bubble, which is formed either in the tubes C or K, having a tendency to ascend proportional to its lightness as compared with water, necessarily rushes upwards; if in C towards A, and if in K towards H. But this motion of the steam is also aided by the rapid circulation of the water which is continually maintained [Pg427] in the tubes, otherwise it might be possible, notwithstanding the levity of steam compared with water, that a bubble might remain in a narrow tube without rising. To bring the matter to the test of experiment, I have connected two cylinders, such as D and H, by a system of glass tubes, such as represented at C E K. The rapid and constant circulation of the water was then made evident: bubbles of steam were formed in the tubes, it is true; but they passed with great rapidity into the upper cylinder, and rose to the surface, so that the glass tubes never acquired a higher temperature than that of the water which passed through them.

Every part of the boiler being cylindrical, it has the form which, mechanically considered, is most favourable to strength, and which, within given dimensions, contains the greatest quantity of water. It is also free from the defects arising from unequal expansion, which are found to be most injurious in tubular boilers. The tubes C and K can freely expand in the direction of their length, without being loosened at their joints, and without straining any part of the apparatus; the tubes E, being short, are subject to a very slight degree of expansion; and it is obvious that the long tubes, with which they are connected, will yield to this without suffering a strain, and without causing any part of the apparatus to be loosened.

When water is converted into steam, any foreign matter which may be combined with it is disengaged, and is deposited on the bottom of the vessel in which the water is evaporated. All boilers, therefore, require occasional cleansing, to prevent the crust thus formed from accumulating; and this operation, for obvious reasons, is attended with peculiar difficulty in tubular boilers. In the case before us, the crust of deposited matter would gather and thicken in the tubes C and K, and if not removed, would at length choke them. But besides this, it would be attended with a still worse effect; for, being a bad conductor, it would intercept the heat in its transit from the fire to the water, and would cause the metal of the tube to become unduly heated. Mr. Gurney of course foresaw this inconvenience, and contrived an ingenious chemical method of removing it, by occasionally injecting [Pg428] through the tubes such an acid as would combine with the deposit, and carry it away. This method was effectual; and although its practical application was found to be attended with difficulty in the hands of common workmen, Mr. Gurney was persuaded to adhere to it by the late Dr. Wollaston, until experience proved the impossibility of getting it effectually performed, under the circumstances in which boilers are commonly used. Mr. Gurney then adopted a method of removing the deposit by mechanical means. Opposite the mouths of the tubes, and on the other side of the cylinders D and H, are placed a number of holes, which, when the boiler is in use, are stopped by pieces of metal screwed into them. When the tubes require to be cleaned, these stoppers are removed, and an iron scraper is introduced through the holes into the tubes, which, being passed backwards and forwards, removes the deposit.

In these engines the draught through the furnace was produced by projecting the waste steam up the chimneys as is practised in railway engines; a method so perfectly effectual, that it is unlikely to be superseded by any other. The objection which has been urged against it in locomotive engines, working on turnpike-roads, is, that the noise which it produces has a tendency to frighten horses.

In the engines on the Liverpool road, the steam is allowed to pass directly from the eduction pipe of the cylinder to the chimney, and it there escapes in puffs corresponding with the alternate motion of the pistons, and produces a noise, which, although attended with no inconvenience on the railroad, would perhaps be objectionable on turnpike-roads. In the engine used in Mr. Gurney's steam-carriage, the steam which passes from the cylinders is conducted to a receptacle, which he calls a blowing box. This box serves the same purpose as the upper chamber of a smith's bellows. It receives the steam from the cylinders in alternate puffs, but lets it escape into the chimney in a continued stream by a number of small jets. Regular draught is by this means produced, and no noise is perceived. Another exit for the steam is also provided, by which the conductor is enabled to increase or diminish, or to suspend altogether, the draught [Pg429] in the chimney, so as to adapt the intensity of the fire to the exigencies of the road. This is a great convenience in practice; because on some roads a draught is scarcely required, while on others a powerful blast is indispensable.

Connected with this blowing box is another apparatus of considerable practical importance. The pipe through which the feeding water is conducted from the tank is carried through this blowing box, within which it is coiled in a spiral form, so that an extensive thread of the water is exposed to the heat of the waste steam which has escaped from the cylinders, and which is enclosed in this blowing box. In passing through this pipe the feeding water is raised from the ordinary temperature of about 60° to the temperature of 212°. Fuel is thus economised and weight diminished; but there is another still greater advantage attending this process. The feeding water in the worm just mentioned, while it takes up the heat from the surrounding steam in the blowing box, condenses a part of the waste steam, which is thence conducted to the tank, from which the feeding water is pumped.

When steam is generated so rapidly as is necessarily the case in locomotive boilers, it rises with great violence in numerous bubbles from the bottom of the boiler to the surface of the water, and puts the liquid into a state of foaming turbulence not unlike the sea in a storm. As the steam rushes from the surface into the upper part of the boiler, under these circumstances, it carries with it a spray by which water is scattered in minute subdivision among the steam, and floats there like the spray which rises from the base of a cascade. If the steam be conducted immediately to the cylinder from the boiler in this state, it will carry with it the water which is thus suspended in it, which will pass through the cylinder, and finally be driven into the atmosphere upon the returning stroke of the piston. The hot water thus carried off possesses none of the mechanical properties of steam, and is wholly inefficient as a moving power, and is therefore an extensive source of the waste of heat. In every boiler, some means should be provided for the separation of the water thus suspended in the steam, before the steam is conducted to the cylinder. In ordinary boilers, the large space which [Pg430] remains above the surface of the water serves this purpose. The steam being there subject to no agitation or disturbance, the water mechanically suspended in it descends by its own gravity, and leaves pure steam in the upper part. In the small tubular boilers, this has been a matter, however, of greater difficulty. The contracted space in which the ebullition takes place causes the water to be mixed with the steam in a greater quantity than could happen in common boilers; and the want of the same steam-room renders the separation of the water from the steam a matter of some difficulty. These inconveniences have been attempted to be overcome by various contrivances. I have already described the rapid and regular circulation effected by the arrangement of the tubes. By this a regularity in the currents is established, which has a tendency to diminish the mixture of water with the steam. In addition to this, a method of separation is provided in the vessel I, which is a strong iron cylinder of some magnitude, placed out of the immediate influence of the fire. A partial separation of the steam from the water takes place in the cylinder H; and the steam with the water mechanically suspended in it, technically called moist steam, rises into the _separator_ I. Here, being free from all agitation and currents, and being, in fact, quiescent, the particles of water fall to the bottom, while the pure steam remains at the top. This separator, therefore, serves all the purposes of the steam-room above the surface of the water in the large plate boilers. The dry steam is thus collected and ready for the supply of the engine through the tube N, while the water, which is disengaged from it, is collected at the bottom of the separator, and is conducted through the tube T to the lowest vessel D, to be again circulated through the boiler.

The pistons of the engine work on the axles of the hind wheels of the carriage which bears the engine, by cranks, as in the locomotives on the Manchester railway, so that the axle is kept in a constant state of rotation while the engine is at work. The wheels placed on this axle are not permanently fixed or keyed upon it, as in the Manchester locomotives; but they are capable of turning upon it in the same manner as ordinary carriage wheels. Immediately within [Pg431] these wheels there are fixed upon the axles two projecting spokes or levers, which revolve with the axle, and which take the position of two opposite spokes of the wheel. These may be occasionally attached to the wheel or detached from it; so that they are capable of compelling the wheels to turn with the axle, or leaving the axle free to turn independently of the wheel, or the wheel independent of the axle, at the pleasure of the conductor. It is by these levers that the engine is made to propel either or both of the wheels. If both pairs of spokes are thrown into connexion with the wheels, the crank shaft or axle will cause both wheels to turn with it, and in that case the operation of the carriage is precisely the same as those of the locomotives already described upon the Liverpool and Manchester line; but this is rarely found to be necessary, since the adhesion of one wheel with the road is generally sufficient to propel the carriage, and consequently only one pair of these fixed levers are used, and the carriage propelled by only one of the two hind wheels. The fore wheels of the carriage turn upon a pivot similar to those of a four-wheeled coach. The position of these wheels is changed at pleasure by a pinion and circular rack, which is moved by the conductor, and in this manner the carriage is guided with precision and facility.

The force of traction necessary to propel a carriage upon common roads must vary with the variable quality of the road, and consequently the propelling power, or the pressure upon the pistons of the engine, must be susceptible of a corresponding variation; but a still greater variation becomes necessary from the undulations and hills which are upon all ordinary roads. This necessary change in the intensity of the impelling power is obtained by restraining the steam in the boiler by the throttle-valve, as already described in the locomotive engines on the railroad. This principle, however, is carried much further in the present case. The steam in the boiler maybe at a pressure of from 100 to 200 lbs. on the square inch; while the steam on the working piston may not exceed 30 or 40 lbs. on the inch. Thus an immense increase of power is always at the command of the conductor; so that when a hill is encountered, or a rough piece of road, [Pg432] he is enabled to lay on power sufficient to meet the exigency of the occasion.

The two difficulties which have been always apprehended in the practical working of steam-carriages upon common roads are, first, the command of sufficient power for hills and rough pieces of road; and, secondly, the apprehended insufficiency of the adhesion of the wheels with the road to propel the carriage. The former of these difficulties has been met by allowing steam of very great pressure to be constantly maintained in the boiler with perfect safety. As to the second, all experiments tend to show that there is no ground for the supposition that the adhesion of the wheels is in any case insufficient for the purposes of propulsion. Mr. Gurney states, that he has succeeded in driving carriages thus propelled, up considerable hills on the turnpike roads about London. He made a journey to Barnet with only one wheel attached to the axle, which was found sufficient to propel the carriage up all hills upon that road. The same carriage, with only one propelling wheel, also went to Bath, and surmounted all the hills between Cranford Bridge and Bath, going and returning.

A double stroke of the piston produces one revolution of the propelling wheels, and causes the carriage to move through a space equal to the circumference of those wheels. It will therefore be obvious, that the greater the diameter of the wheels, the better adapted the carriage is for speed; and, on the other hand, wheels of smaller diameter are better adapted for power. In fact, the propelling power of an engine on the wheels will be in the inverse proportion of their diameter. In carriages designed to carry great weights at a moderate speed, smaller wheels will be used; while in those intended for the transport of passengers at considerable velocities, wheels of at least 5 feet diameter are most advantageous.

(205.) Among the numerous popular prejudices to which this new invention has given rise, one of the most mischievous in its effects and most glaring in its falsehood, is the notion that carriages thus propelled are more injurious to roads than carriages drawn by horses. This error has been successfully exposed in the evidence taken before the committee of the [Pg433] House of Commons upon steam carriages. It is there demonstrated, not only that carriages thus propelled do not wear a turnpike road more rapidly than those drawn by horses, but that, on the other hand, the wear by the feet of horses is far more rapid and destructive than any which could be produced by the wheels of carriages. Steam carriages admit of having the tires of the wheels broad, so as to act upon the road more in the manner of rollers, and thereby to give consistency and firmness to the material of which the road is composed. The driving wheels being proved not to slip upon the road, do not produce any effects more injurious than the ordinary rolling wheels; consequently the wear occasioned by a steam carriage upon a road, is not more than that produced by a carriage drawn by horses, of an equivalent weight and the same or equal tires; but the wear produced by the pounding and digging of horses' feet in draught is many times greater than that produced by the wear of any carriage. Those who still have doubts upon this subject, if there be any such persons, will be fully satisfied by referring to the evidence which accompanies the report of the committee of the House of Commons, printed in October, 1831.

The weight of machinery necessary for steam carriages is sometimes urged as an objection to their practical utility. Mr. Gurney states, that, by successive improvements in the details of the machinery, the weight of his carriages, without losing any of the propelling power, may be reduced to 35 cwt., exclusive of the load, and fuel and water: but thinks that it is possible to reduce the weight still further.

A steam carriage constructed by Mr. Gurney, weighing 35 cwt., working for 8 hours, is found, according to his statement, to do the work of about 30 horses. He calculates that the weight of his propelling carriage, which would be capable of drawing 18 persons, would be equal to the weight of 4 horses; and the carriage in which these persons would be drawn would have the same weight as a common stage coach capable of carrying the same number of persons. Thus the weight of the whole—the propelling carriage and the carriage for passengers taken together—would be the same [Pg434] with the weight of a common stage coach, with 4 horses inclusive.

There are two methods of applying locomotives upon common roads to the transport of passengers or goods; the one is by causing the locomotive to carry, and the other to draw the load; and different projectors have adopted the one and the other method. Each is attended with its advantages and disadvantages. If the same carriage transport the engine and the load, the weight of the whole will be less in proportion to the load carried; also a greater pressure may be produced on the wheels by which the load is propelled. It is also thought that a greater facility in turning and guiding the vehicle, greater safety in descending the hills, and a saving in the original cost, will be obtained. On the other hand, when the passengers are placed in the same carriage with the engine, they are necessarily more exposed to the noise of the machinery and to the heat of the boiler and furnace. The danger of explosion is so slight, that, perhaps, it scarcely deserves to be mentioned; but still _the apprehension_ of danger on the part of the passengers, even though groundless, should not be disregarded. This apprehension will be obviously removed or diminished by transferring the passengers into a carriage separate from the engine; but the greatest advantage of keeping the engine separate from the passengers is the facility which it affords of changing one engine for another in case of accident or derangement on the road, in the same manner as horses are changed at the different stages: or, if such an accident occur in a place where a new engine cannot be procured, the load of passengers may be carried forward by horses, until it is brought to some station where a locomotive may be obtained. There is also an advantage arising from the circumstance, that when the engines are under repair, or in process of cleaning, the carriages for passengers are not necessarily idle. Thus the same number of carriages for passengers will not be required when the engine is used to draw as when it is used to carry.

In case of a very powerful engine being used to carry great loads, it would be quite impracticable to place the engine [Pg435] and loads on four wheels, the pressure being such as no turnpike road could bear. In this case it would be indispensably necessary to place a part of the load at least upon separate carriages to be drawn by the engine.

In the comparison of carriages propelled by steam with carriages drawn by horses, there is no respect in which the advantage of the former is so apparent as the safety afforded to the passenger. Steam power is under the most perfect control, and a carriage thus propelled is capable of being guided with the most admirable precision. It is also capable of being stopped almost suddenly, whatever be its speed: it is capable of being turned within a space considerably less than that which would be necessary for four-horse coaches. In turning sharp corners, there is no danger, with the most ordinary care on the part of the conductor. On the other hand, horse power, as is well known, is under very imperfect control, especially when horses are used adapted to that speed which at present is generally considered necessary for the purposes of travelling. "The danger of being run away with and overturned," says Mr. Farey, in his evidence before the House of Commons, "is greatly diminished in a steam coach. It is very difficult to control four such horses as can draw a heavy stage coach ten miles an hour, in case they are frightened or choose to run away; and, for such quick travelling, they must be kept in that state of courage that they are always inclined to run away,

## particularly down hill, and at sharp turns in the road. Steam

power has very little corresponding danger, being perfectly controllable, and capable of having its power reversed, to retard in going down hill. It must be carelessness that would occasion the overturning of a steam carriage. The chance of breaking down has been hitherto considerable, but it will not be more than in stage coaches when the work is truly proportioned and properly executed. The risk from explosion of the boiler is the only new cause of danger, and that I consider not equivalent to the danger from horses."

That the risk of accident from explosion is extremely slight, may be proved by the fact that the railway between Liverpool and Manchester has now been in operation for about ten [Pg436] years, and that other railways more extensive in length have been worked for a considerable time, and that no instance has ever yet occurred of an accident to passengers from the explosion of a boiler. Generally these machines, when they fail, are attended with no other effect than the extinction of the fire, by the water of the boiler flowing in upon it. I am not aware of more than one instance, in which a serious accident has been produced by explosion; and in that instance, the sufferers were only the engineer and stoker. In the steam-engine of Mr. Gurney, the carriage is drawn after the engine, as represented in _fig._ 117.

[Illustration: _Fig._ 117.]

[Illustration: _Fig._ 118.]

(206.) In the boiler to be used in the steam carriage projected by Mr. Walter Hancock, the subdivision of the water is accomplished by dividing a case or box by a number of [Pg437] thin plates of metal, like a galvanic battery, the water being allowed to flow between every alternate pair of plates, at E, _fig._ 118., and the intermediate spaces H forming the flue through which the flame and hot air are propelled.

In fact, a number of thin plates of water are exposed on both sides to the most intense action of flame and heated air; so that steam of a high pressure is produced in great abundance and with considerable rapidity. The plates forming the boiler are bolted together by strong iron ties, extending across the boiler, at right angles to the plates, as represented in the figure. The distance between the plates is two inches.

There are ten flat chambers of this kind for water, and intermediately between them ten flues. Under the flues is the fire-place, or grate, containing six square feet of fuel in vivid combustion. The chambers are all filled to about two thirds of their depth with water, and the other third is left for steam. The water chambers, throughout the whole series, communicate with each other both at top and bottom, and are held together by two large bolts. By releasing these bolts, at any time, the chambers fall asunder; and by screwing them up they may be all made tight again. The water is supplied to the boiler by a forcing-pump, and the steam issues from the centre of one of the flues at the top.

These boilers are constructed to bear a pressure of 400 or 500 lbs. on the square inch; but the average pressure of the steam on the safety valve is from 60 to 100. There are 100 square feet of surface in contact with the water exposed to the fire. The stages which such an engine performs are eight miles, at the end of which a fresh supply of fuel and water are taken in. It requires about two bushels of coke for each stage.

The steam carriage of Mr. Hancock differs from that of Mr. Gurney in this—that in the former the passengers and engine are all placed on the same carriage. The boiler is placed behind the carriage; and there is an engine-house between the boiler and the passengers, the latter being placed in the fore part of the vehicle; so that all the machinery is behind them. The carriages are adapted to carry 14 [Pg438] passengers, and weigh, exclusive of their load, about 3-1/2 tons, the tires of the wheels being about 3-1/2 inches in breadth. Mr. Hancock states, that the construction of his boiler is of such a nature, that, even in the case of bursting, no danger is to be apprehended, nor any other inconvenience than the stoppage of the carriage. He states that, while travelling about nine miles an hour, and working with a pressure of about 100 lbs. on the square inch, loaded with thirteen passengers, the carriage was suddenly stopped. At first the cause of the accident was not apparent; but, on opening one of the cocks of the boiler, it was found that it contained neither steam nor water. Further examination proved that the boiler had burst. On unscrewing the bolts, it was found that there were several large holes in the plates of the water-chamber, through which the water had flowed on the fire, but neither noise nor explosion, nor any dangerous consequences, ensued.

(207.) Mr. Nathaniel Ogle of Southampton obtained a patent for a locomotive carriage, and worked it for some time experimentally; but as his operations do not appear to have been continued, I suppose he was unsuccessful in fulfilling those conditions, without which the machine could not be worked with economy and profit. In his evidence before a committee of the House of Commons, he has thus described his contrivance:—

"The base of the boiler and the summit are composed of cross pieces, cylindrical within and square without; there are holes bored through these cross pieces, and inserted through the whole is an air tube. The inner hole of the lower surface, and the under hole of the upper surface, are rather larger than the other ones. Round the air tube is placed a small cylinder, the collar of which fits round the larger aperture on the inner surface of the lower frame, and the under surface of the upper frame-work. These are both drawn together by screws from the top; these cross pieces are united by connecting pieces, the whole strongly bolted together; so that we obtain, in one tenth of the space, and with one tenth of the weight, the same heating surface and power as is now obtained in other and low-pressure boilers, with incalculably [Pg439] greater safety. Our present experimental boiler contains 250 superficial feet of heating surface in the space of 3 feet 8 inches high, 3 feet long, and 2 feet 4 inches broad, and weighs about 8 cwt. We supply the two cylinders with steam, communicating by their pistons with a crank axle, to the ends of which either one or both wheels are affixed as may be required. One wheel is found to be sufficient, except under very difficult circumstances, and when the elevation is about one foot in six to impel the vehicle forward.

"The cylinders of which the boiler is composed are so small as to bear a greater pressure than could be produced by the quantity of fire beneath the boiler; and if any one of these cylinders should be injured by violence, or any other way, it would become merely a safety valve to the rest. We never, with the greatest pressure, burst, rent, or injured our boiler; and it has not once required cleaning, after having been in use twelve months."

Dr. Church of Birmingham has obtained a succession of patents for contrivances connected with a locomotive engine for stone roads; and a company, consisting of a considerable number of individuals, possessing sufficient capital, has been formed in Birmingham, for carrying into effect his designs, and working carriages on his principle. The present boiler of Dr. Church is formed of copper. The water is contained between two sheets of copper, united together by copper nails, in a manner resembling the way in which the cloth forming the top of a mattress or cushion is united with the cloth which forms the bottom of it, except that the nails or pins, which bind the sheets of copper, are much closer together. The water, in fact, seems to be "quilted" or "padded" in between two sheets of thin copper. This double sheet of copper is formed into an oblong rectangular box, the interior of which is the fire-place and ash-pit, and over the end of which is the steam-chest. The great extent of surface exposed to the immediate

## action of the fire causes steam to be produced with great

rapidity.

Various other projects for the application of steam engines on common roads were in a state of progressive improvement, [Pg440] when the greater advantages attending railways were considered so manifest, that considerable doubts were raised, whether, supposing the problem of the application of the steam engine on common roads to be successfully solved, it could ever be attended with the same economy and effect, as by the adoption of a railway. Among the projects which promised a successful issue, may be mentioned the locomotive engines contrived by Messrs. Maudslay and Field, by Colonel Maceroni, and by Mr. Scott Russell. These and others have, however, been abandoned, mainly, we believe, from the impression, that wherever traffic can exist, sufficiently extensive to render the application of steam power profitable, a railway must always supersede a common road; and that, even in the limited traffic to be expected on branches to the great railways, horse power applied to railways would be attended with more economy than steam power applied on stone roads.

[Illustration]

[Pg441]

[Illustration]

CHAP. XIII.

STEAM NAVIGATION.

FORM AND ARRANGEMENT OF MARINE ENGINES. — EFFECTS OF SEA WATER IN BOILERS. — REMEDIES FOR THEM. — BLOWING OUT. — INDICATORS OF SALTNESS. — SEAWARD'S INDICATOR. — HIS METHOD OF BLOWING OUT. — FIELD'S BRINE PUMPS. — TUBULAR CONDENSERS APPLIED BY MR. WATT. — HALL'S CONDENSERS. — COPPER BOILERS. — PROCESS OF STOKING. — MARINE BOILERS. — MEANS OF ECONOMISING FUEL. — COATING MARINE BOILERS WITH FELT. — NUMBER AND ARRANGEMENT OF FURNACES AND FLUES. — HOWARD'S ENGINE. — APPLICATION OF THE EXPANSIVE PRINCIPLE IN MARINE ENGINES. — RECENT IMPROVEMENTS OF MESSRS. MAUDSLAY AND FIELD. — HUMPHRYS' ENGINE. — COMMON PADDLE-WHEEL. — FEATHERING PADDLES. — MORGAN'S WHEELS. — THE SPLIT PADDLE. — PROPORTION OF POWER TO TONNAGE. — IMPROVED EFFICIENCY OF MARINE ENGINES. — IRON STEAM-VESSELS. — STEAM-NAVIGATION TO INDIA.

(208.) Among the many ways in which the steam-engine has ministered to the advancement of civilisation and the social progress of the human race, there is none more [Pg442] important or more interesting than its application to navigation. Before it lent its giant powers to the propulsion of ships, locomotion over the waters of the deep was attended with so much danger and uncertainty that, as a common proverb, it became the type and the representative of every thing which was precarious and perilous. The application, however, of steam to navigation has rescued the mariner and the voyager from many of the dangers of wind and water; and even in its present state, putting out of view its probable improvement, it has rendered all voyages of moderate length as safe, and very nearly as regular, as journeys over-land. As a means of transport by sea, the application of this power may be considered as established; and it is now receiving improvements by which its extension to the longest class of ocean voyages is a question not of practicability, but merely of profit.

The manner in which the steam-engine is rendered an instrument for the propulsion of vessels must in its general features be so familiar to every one as to require but short explanation. A shaft is carried across the vessel, being continued on either side beyond the timbers: to the extremities of this shaft, on the outside of the vessel, are fixed a pair of wheels constructed like undershot water-wheels, having attached to their rims a number of flat boards called _paddle-boards_. As the wheels revolve, these paddle-boards strike the water, driving it in a direction contrary to that in which it is intended the vessel should be propelled. The moving force imparted to the water thus driven backwards is necessarily accompanied by a re-action upon the vessel through the medium of the paddle-shaft, by which the vessel is propelled forwards. On the paddle-shaft two cranks are constructed, similar to the cranks already described on the axle of the driving wheels of a locomotive engine. These cranks are placed at right angles to each other, so that when either is in its highest or lowest position the other shall be horizontal. They are driven by two steam-engines, which are placed in the hull of the vessel below the paddle-shaft. In the earlier steam-boats a single steam-engine was used, and in that case the unequal action of the engine on the crank was equalised by a fly-wheel. This, however, has been long [Pg443] since abandoned in European vessels, and the use of two engines is now almost universal. By the relative position of the cranks it will be seen, that when either crank is at its dead points, the other will be in the positions most favourable to its

## action, and in all intermediate positions the relative efficiency

of the cranks will be such as to render their combined action very nearly uniform.

The steam-engines used to impel vessels may be either condensing engines, similar to those of Watt, and such as are used in manufactures generally, or they may be non-condensing and high-pressure engines, similar in principle to those used on railways. Low-pressure condensing engines are, however, universally used for marine purposes in Europe and to some extent in the United States. In the latter country, however, high-pressure engines are also in pretty general use, on rivers where lightness is a matter of importance.

The arrangement of the parts of a marine engine differs in some respects from that of a land engine. The limitation of space, which is unavoidable in a vessel, renders greater compactness necessary. The paddle-shaft on which the cranks to be driven by the engine are constructed being very little below the deck of the vessel, the beam and connecting rod could not be placed in the position in which they usually are in land engines, without carrying the machinery to a considerable elevation above the deck. This is done in the steam-boat engines used on the American rivers; but it would be inadmissible in steam-boats in general, and more especially in sea-going steamers. The connecting rods, therefore, instead of being presented downwards towards the cranks which they drive, must, in steam-vessels, be presented upwards, and the impelling force received from below. If, under these circumstances, the beam were in the usual position above the cylinder and piston-rod, it must necessarily be placed between the engine and the paddle-shaft. This would require a depth for the machinery which would be incompatible with the magnitude of the vessel. The beam, therefore, of marine engines, instead of being above the cylinder and piston, is placed below them. To the top of the [Pg445] piston-rods cross pieces are attached of greater length than the diameter of the cylinders, so that their extremities shall project beyond the cylinders. To the ends of these cross pieces are attached by joints the rods of a parallel motion: these rods are carried downwards, and are connected with the ends of two beams below the cylinder, and placed on either side of it. The opposite ends of these beams are connected by another cross piece, to which is attached a connecting rod, which is continued upwards to the crank-pin, to which it is attached, and which it drives. Thus the beam, parallel motion, and connecting rod of a marine engine, is similar to that of a land engine, only that it is turned upside down; and in consequence of the impossibility of placing the beam directly over the piston-rod, two beams and two systems of parallel motion are provided, one on each side of the engine, acted upon by, and

## acting on the piston-rod and crank by cross pieces.

The proportion of the cylinders differs from that usually observed in land engines, for like reasons. The length of the cylinder of land engines is generally greater than its diameter, in the proportion of about two to one. The cylinders of marine engines are, however, commonly constructed with a diameter very little less than their length. In proportion, therefore, to their power their stroke is shorter, which infers a corresponding shortness of crank and a greater limitation of play of all the moving parts in the vertical direction. The valves and the gearing by which they are worked, the air-pump, the condenser, and other parts of the marine engines, do not materially differ from those already described in land engines.

[Illustration: _Fig._ 119.]

These arrangements of a marine engine will be more clearly understood by reference to _fig._ 119.[35], in which is represented a longitudinal section of a marine engine with its boiler as placed in a steam-vessel. The sleepers of oak, supporting the engine, are represented at X, the base of the engine being secured to these by bolts passing through them [Pg446] and the bottom timbers of the vessel; S is the steam-pipe leading from the steam-chest in the boiler to the slides _c_, by which it is admitted to the top and bottom of the cylinder. The condenser is represented at B, and the air-pump at E. The hot well is seen at F, from which the feed is taken for the boiler; L is the piston-rod connected by the parallel motion _a_ with the beam H, working on a centre K, near the base of the engine. The other end of the beam I drives the connecting rod M, which extends upwards to the crank which it works upon the paddle-shaft O. Q R is the framing by which the engine is supported. The beam here exhibited is shown on dotted lines as being on the further side of the engine. A similar beam similarly placed, and moving on the same axis, must be understood to be at this side connected with the cross head of the piston in like manner by a parallel motion, and with a cross piece attached to the lower end of the connecting rod and to the opposite beam. The eccentric which works the slides is placed upon the paddle shaft O, and the connecting arm which drives the slides may be easily detached when the engine requires to be stopped. The section of the boiler, grate, and flues, is represented at W U. The safety-valve _y_ is enclosed beneath a pipe carried up beside the chimney, and is inaccessible to the engine-man; _h_ are the cocks for blowing the salted water from the boiler; and I I the feed-pipe.

The general arrangement of the engine-room of a steam-vessel is represented in _fig._ 120.

The nature of the effect required to be produced by marine engines does not render either necessary or possible that great regularity of action which is indispensable in a steam-engine applied to the purposes of manufacture. The agitation of the surface of the sea will cause the immersion of the paddle-wheels to be subject to great variation, and the resistance produced by the water to the engine will undergo a corresponding change. The governor, therefore, and other parts of the apparatus, contrived for giving to the engine that great regularity required in manufactures, are omitted in nautical engines, and nothing is introduced save what is [Pg447] necessary to maintain the machine in its full working efficiency.

[Illustration: _Fig._ 120.]

[Illustration: _Fig._ 121.]

To save space, marine boilers are constructed so as to produce the necessary quantity of steam within the smallest possible dimensions. With this view a more extensive surface in proportion to the capacity of the boiler is exposed to the action of the fire. The flues, by which the flame and heated air are conducted to the chimney, are so constructed that the heat may act upon the water on every side in thin oblong shells or plates. This is accomplished by constructing the flues so as to traverse the boiler backwards and forwards several times before they terminate [Pg448] in the chimney. Such an arrangement renders the expense of the boilers greater, but their steam-producing power is proportionally augmented, and experiments made by Mr. Watt, at Birmingham, have proved that such boilers with the same consumption of fuel will produce, as compared with common land boilers, an increased evaporation in the proportion of about three to two.

[Illustration: _Fig._ 122.]

[Illustration: _Fig._ 123.]

The form and arrangement of the water-spaces and flues in marine boilers may be collected from the sections of the boilers used in some of the government steamers, exhibited in _figs._ 121, 122, 123. A section made by a horizontal plane passing through the flues is exhibited in _fig._ 121. The furnaces F communicate in pairs with the flues E, the air following the course through the flues represented by the arrows. The flue E passes to the back of the boiler, then returns to the front, then to the back again, and is finally carried back to the front, where it communicates at C with the curved flue B, represented in the transverse vertical section, _fig._ 122. This curved flue B finally terminates in the chimney A. There are in this case three independent boilers, each worked by two furnaces communicating with the same system of flues; and in the curved flues B, _fig._ 122., by which the air is finally conducted through the chimney, are placed three independent [Pg449] dampers, by means of which the furnace of each boiler can be regulated independently of the other, and by which each boiler may be separately detached from communication with the chimney. The letters of reference in the horizontal section, _fig._ 121., correspond with those in the transverse vertical section, _fig._ 122., E representing the commencement of the flues, and C their termination.

[Illustration: _Fig._ 124.]

A longitudinal section of the boiler made by a vertical plane extending from the front to the back is given in _fig._ 123., where F, as before, is the furnace, G the grate-bars sloping downwards from the front to the back, H the fire-bridge, C the commencement of the flues, and A the chimney. An elevation of the front of the boiler is represented in _fig._ 124., showing two of the fire-doors closed, and the other two removed, displaying the position of the grate-bars in front. Small openings are also provided, closed by proper doors, by which access can be had to the under side of the flues between the foundation timbers of the engine for the purpose of cleaning them.

Each of these boilers can be worked independently of the others. By this means, when at sea, the engine may be worked by any two of the three boilers, while the third is being cleaned and put in order. In all sea-going steamers multiple boilers are at present provided for this purpose.

In the boilers here represented the flues are all upon the same level, winding backwards and forwards without passing one above the other. In other boilers, however, the flues, [Pg450] after passing backwards and forwards near the bottom of the boiler, turn upwards and pass backwards and forwards through a level of the water nearer its surface, finally terminating in the chimney. More heating surface is thus obtained with the same capacity of boiler.

The most formidable difficulty which has been encountered in the application of the steam-engine to sea-voyages has arisen from the necessity of supplying the boiler with sea-water instead of pure fresh water. The sea-water is injected into the condenser for the purpose of condensing the steam, and it is thence, mixed with the condensed steam, conducted as feeding water into the boiler.

(209.) Sea-water holds, as is well known, certain alkaline substances in solution, the principal of which is muriate of soda, or common salt. Ten thousand grains of pure sea-water contain two hundred and twenty grains of common salt, the remaining ingredients being thirty-three grains of sulphate of soda, forty-two grains of muriate of magnesia, and eight grains of muriate of lime. The heat which converts pure water into steam does not at the same time evaporate those salts which the water holds in solution. As a consequence it follows, that as the evaporation in the boiler is continued, the salt, which was held in solution by the water which has been evaporated, remains in the boiler, and enters into solution with the water remaining in it. The quantity of salt contained in sea-water being considerably less than that which water is capable of holding in solution, the process of evaporation for some time is attended with no other effect than to render the water in the boiler a stronger solution of salt. If, however, this process be continued, the quantity of salt retained in the boiler having constantly an increasing proportion to the quantity of water, it must at length render the water in the boiler a saturated solution—that is, a solution containing as much salt as at the actual temperature it is capable of holding in solution. If, therefore, the evaporation be continued beyond this point, the salt disengaged from the water evaporated instead of entering into solution with the water remaining in the boiler will be precipitated in the form of sediment; and if the process be continued in the [Pg451] same manner, the boiler would at length become a mere salt-pan.

But besides the deposition of salt sediment in a loose form, some of the constituents of sea-water having an attraction for the iron of the boiler, collect upon it in a scale or crust in the same manner as earthy matters held in solution by spring-water are observed to form and become incrusted on the inner surface of land-boilers and of common culinary vessels.

The coating of the inner surface of a boiler by incrustation and the collection of salt sediment in its lower parts, are attended with effects highly injurious to the materials of the boiler. The crust and sediment thus formed within the boiler are almost non-conductors of heat, and placed, as they are, between the water contained in the boiler and the metallic plates which form it, they obstruct the passage of heat from the outer surface of the plates in contact with the fire to the water. The heat, therefore, accumulating in the boiler-plates so as to give them a much higher temperature than the water within the boiler, has the effect of softening them, and by the unequal temperature which will thus be imparted to the lower plates which are incrusted, compared with the higher parts which may not be so, an unequal expansion is produced, by which the joints and seams of the boiler are loosened and opened, and leaks produced.

These injurious effects can only be prevented by either of two methods; first, by so regulating the feed of the boiler that the water it contains shall not be suffered to reach the point of saturation, but shall be so limited in its degree of saltness that no injurious incrustation or deposit shall be formed; secondly, by the adoption of some method by which the boiler may be worked with fresh water. This end can only be attained by condensing the steam by a jet of fresh water, and working the boiler continually by the same water, since a supply of fresh water sufficient for a boiler worked in the ordinary way could never be commanded at sea.

(210.) The method by which the saltness of the water in the boiler is most commonly prevented from exceeding a certain [Pg452] limit has been to discharge from the boiler into the sea a certain quantity of over-salted water, and to supply its place by sea-water introduced into the condenser through the injection-cock for the purpose of condensing the steam, this water being mixed with the steam so condensed, and being, therefore, a weaker solution of salt than common sea-water. To effect this, cocks called _blow-off cocks_, are usually placed in the lower parts of the boiler, where the over-salted, and therefore heavier, parts of the water collect. The pressure of the steam and incumbent weight of the water in the boiler force the lower strata of water out through these cocks; and this process, called _blowing out_, is, or ought to be, practised at such intervals as will prevent the water from becoming over salted. When the salted water has been blown out in this manner, the level of the water in the boiler is restored by a feed of corresponding quantity.

This process of blowing out, on the due and regular observance of which the preservation and efficiency of the boiler mainly depend, is too often left at the discretion of the engineer, who is, in most cases, not even supplied with the proper means of ascertaining the extent to which the process should be carried. It is commonly required that the engineer should blow out a certain portion of the water in the boiler every two hours, restoring the level by a feed of equivalent amount; but it is evident that the sufficiency of the process founded on such a rule must mainly depend on the supposition that the evaporation proceeds always at the same rate, which is far from being the case with marine boilers. An indicator, by which the saltness of the water in the boiler would always be exhibited, ought to be provided, and the process of blowing out should be regulated by the indications of that instrument. To blow out more frequently than is necessary is attended with a waste of fuel; for hot water is thus discharged into the sea while cold water is introduced in its place, and consequently all the heat necessary to produce the difference of the temperatures of the water blown out and the feed introduced is lost. If, on the other hand, the process of blowing out be observed less frequently than is necessary, then more or less incrustation and deposit [Pg453] may be produced, and the injurious effects already described ensue.

As the specific gravity of water holding salt in solution is increased with every increase of the strength of the solution, any form of hydrometer capable of exhibiting a visible indication of the specific gravity of the water contained in the boiler would serve the purpose of an indicator, to show when the process of blowing out is necessary, and when it has been carried to a sufficient extent. The application of such instruments, however, would be attended with some practical difficulties in the case of sea-boilers.

The temperature at which a solution of salt boils under a given pressure varies considerably with the strength of the solution; the more concentrated the solution is, the higher will be its boiling temperature under the same pressure. A comparison, therefore, of a steam-gauge attached to the boiler, and a thermometer immersed in it, showing the pressure and the temperature, would always indicate the saltness of the water; and it would not be difficult so to graduate these instruments as to make them at once show the degree of saltness.

If the application of the thermometer be considered to be attended with practical difficulty, the difference of pressures under which the salt water of the boiler and fresh water of the same temperature boil, might be taken as an indication of the saltness of the water in the boiler, and it would not be difficult to construct upon this principle a self-registering instrument, which would not only indicate but record from hour to hour the degree of saltness of the water. A small vessel of distilled water being immersed in the water of the boiler would always have the temperature of that water, and the steam produced from it communicating with a steam-gauge, the pressure of such steam would be indicated by that gauge, while the pressure of the steam in the boiler under which pressure the salted water boils might be indicated by another gauge. The difference of the pressures indicated by the two gauges would thus become a test by which the saltness of the water in the boiler would be measured. The two pressures might be made to act on opposite ends of the same column of [Pg454] mercury contained in a siphon tube, and the difference of the levels of the two surfaces of the mercury would thus become a measure of the saltness of the water in the boiler. A self-registering instrument founded on this principle formed part of the self-registering steam-log which I proposed to introduce into steam-vessels some time since.

(211.) The Messrs. Seaward of Limehouse have adopted, in some of their recently constructed engines, a method of indicating the saltness of the water, and of measuring the quantity of salted water or brine discharged, by blowing out. A glass-gauge, similar in form to that already described in land engines (156.), is provided to indicate the position of the surface of the water in the boiler. In this gauge two hydrometer balls are provided, the weight of which in proportion to their magnitude is such that they would both sink to the bottom in a solution of salt of the same strength as common sea-water. When the quantity of salt exceeds 5/32 parts of the whole weight of the water, the lighter of the two balls will float to the top; and when the strength is further increased until the proportion of salt exceeds 6/32 parts of the whole, then the heavier ball will float to the top. The actual quantity of salt held in solution by sea-water in its ordinary state is 1/32 part of its whole weight; and when by evaporation the proportion of salt in solution has become 9/32 parts of the whole, then a deposition of salt commences. With an indicator such as that above described, the ascent of the lighter hydrometer ball gives notice of the necessity for blowing out, and the ascent of the heavier may be considered as indicating the approach of an injurious state of saltness in the boiler.

[Illustration: _Fig._ 125.]

The ordinary method of blowing out the salted water from a boiler is by a pipe having a cock in it leading from the boiler through the bottom of the ship, or at a point low down at its side. Whenever the engineer considers that the water in the boiler has become so salted that the process of blowing out should commence, he opens the cock communicating by this pipe with the sea, and suffers an indefinite and uncertain quantity of water to escape. In this way he discharges, according to the magnitude of the boiler, from two to six tons [Pg455] of water, and repeats this at intervals of from two to four hours, as he may consider to be sufficient. If, by observing this process, he prevents the boiler from getting incrusted during the voyage, he considers his duty to be effectually discharged, forgetting that he may have blown out many times more water than is necessary for the preservation of the boiler, and thereby produced a corresponding and unnecessary waste of fuel. In order to limit the quantity of water discharged, Messrs. Seaward have adopted the following method. In _fig._ 125. is represented a transverse section of a part of a steam-vessel; W is the water-line of the boiler, B is the mouth of a blow-off pipe, placed near the bottom of the boiler. This pipe rises to A, and turning in the horizontal direction, A C is conducted to a tank T, which contains exactly a ton of water. This pipe communicates with the tank by a cock D, governed by a lever H. When this lever is moved to D′, the cock D is open, and when it is moved to K, the cock D is closed. From the same tank there proceeds another pipe E, which issues from the side of the [Pg456] vessel into the sea governed by a cock F, which is likewise put in connection with the lever H, so that it shall be opened when the lever H is drawn to the position F′, the cock D′ being closed in all positions of the lever between K and F′. Thus, whenever the cock F communicating with the sea is open, the cock D communicating with the boiler is closed, and _vice versâ_, both cocks being closed when the lever is in the intermediate position K. By this arrangement the boiler cannot, by any neglect in blowing off, be left in communication with the sea, nor can more than a ton of water be discharged except by the immediate act of the engineer. The injurious consequences are thus prevented which sometimes ensue when the blow-off cocks are left open by any neglect on the part of the engineer. When it is necessary to blow off, the engineer moves the lever H, to the position D′. The pressure of the steam in the boiler on the surface of the water W forces the salted water or brine up the pipe B A, and through the open cock C into the tank, and this continues until the tank is filled: when that takes place, the lever is moved from the position D′ to the position F′, by which the cock D is closed, and the cock F opened. The water in the tank flows through the pipe E into the sea, air being admitted through the valve V, placed at the top of the tank, opening inwards. A second ton of brine is discharged by moving the lever back to the position D′, and subsequently returning it to the position F′; and in this way the brine is discharged ton by ton, until the supply of water from the feed which replaces it has caused both the balls in the indicator to sink to the bottom.

(212.) A different method of preserving the requisite freshness of the water in the boiler has been adopted by Messrs. Maudslay and Field, and introduced with success into the Great Western and other steam-vessels. Pumps called _brine-pumps_ are put into communication with the lower part of the boiler, and so constructed as to draw the brine therefrom, and drive it into the sea. These brine-pumps are worked by the engine, and their operation is constant. The feed-pumps are likewise worked by the engine, and they bear such a proportion to the brine-pumps that the quantity of salt discharged in a given time in the brine is equal to the quantity of salt [Pg457] introduced in solution by the water of the feed-pumps. By this means the same actual quantity of salt is constantly maintained in the boiler, and consequently the strength of the solution remains invariable. If the brine discharged by the brine-pumps contains 5/32 parts of salt while the water introduced by the feed-pumps contains only 1/32 part, then it is evident that five cubic feet of the feeding water will contain no more salt than is contained in one cubic foot of brine. Under such circumstances the brine-pumps would be so constructed as to discharge 1/5 of the water introduced by the feed-pumps, so that 4/5 of all the water introduced into the boiler would be evaporated, and rendered available for working the engine.

To save the heat of the brine, a method has been adopted in the marine engines constructed by Messrs. Maudslay and Field similar to one which has been long practised in steam-boilers, and in various apparatus for the warming of buildings. The current of heated brine is conducted from the boiler through a tube which is contained in another, through which the feed is introduced. The warm current of brine, therefore, as it passes out, imparts a considerable portion of its heat to the cold feed which comes in; and it is found that by this expedient the brine discharged into the sea may be reduced to a temperature of about 100°.

This expedient is so effectual that when the apparatus is properly constructed, and kept in a state of efficiency, it may be regarded as nearly a perfect preventive against the incrustation, and the deposition of salt in the boilers, and is not attended with any considerable waste of fuel.

(213.) About the year 1776, Mr. Watt invented a tubular condenser, with a view to condense the steam drawn off from the cylinder without the process of injection. This apparatus consisted of a number of small tubes connecting the top and bottom of the condenser, arranged in a manner not very different from that of the tubes which traverse the boiler of a locomotive engine. These tubes were continually surrounded by cold water, and the steam, as it escaped from the cylinder passing through them, was condensed by their cold surfaces, and collected in the form of water in a reservoir below, from [Pg458] whence it was drawn off by a pump in the same manner as in engines which condensed by injection. One of the advantages proposed by this expedient was, that no atmospheric air would be introduced into the condenser, as is always the case when condensation by injection is practised. Cold water, which is injected, has always combined with it more or less common air. When this water is mixed with the condensed steam, the elevation of its temperature disengages the air combined with it, and this air circulating to the cylinder, vitiates the vacuum. One of the purposes for which the air-pump in condensing steam-engines was provided, and from which it took its name, was to draw off this air. If, however, a tubular condenser could be made to act with the necessary efficiency, no injection water would be introduced for condensation, and the pump would have no other duty except to remove the small quantity of water produced by the condensed steam. That water being subsequently carried back to the boiler by the feed-pumps, a constant system of circulation would be maintained, and the boiler would never require any fresh supply of water, except what might be necessary to make good the waste by leakage and other causes.

This contrivance has been of late years revived by Mr. Samuel Hall of Basford, near Nottingham, with a view to supersede in marine engines the necessity of using sea-water in the boilers. Mr. Hall proposes to make marine boilers with fresh water to condense the steam without injection, by a tubulated condenser, and to provide by the distillation of sea-water the small quantity of fresh water which would be necessary to make good the waste. These condensers have been introduced into several steam-vessels: in some they have been continued, and in others abandoned, and various opinions are entertained of their efficacy. I have not been able to obtain the results of any satisfactory experiments on them, and cannot therefore form a judgment of their usefulness. Mr. Watt abandoned these condensers from finding that the condensation of the steam was not sufficiently sudden, and that consequently at the commencement of the stroke the piston was subject to a resistance which [Pg459] injuriously diminished the amount of the moving power, whereas condensation by jet was almost instantaneous, and the efficiency of the piston throughout the entire stroke was more uniform.

Mr. Watt also found that a fur collected around the tubes of the condenser, so as to obstruct the free passage of heat from the steam to the water of the cold cistern; and that, consequently, the efficiency of the condenser was gradually impaired, and could only be restored by frequent cleansing.

It is stated by Mr. Hall that a vacuum is preserved in his condensers as perfect as that which is maintained in the ordinary condensers by injection. It is objected, on the other hand, that without the injection water and the air which accompanies it being introduced into his condensers, Mr. Hall uses as large and powerful an air-pump as those which are used in engines of equal power condensing by injection; that, consequently, the vacuum which is maintained is produced, not as it ought to be altogether by the condensation of steam, but by the air-pump drawing off the uncondensed steam. To whatever extent this may be true, the efficacy of the machine, as indicated by the barometer-gauge, is only apparent; since as much power is necessary to pump away any portion of uncondensed vapour as is obtained by the vacuum produced by the absence of that vapour.

A tubular condenser of the form proposed by Mr. Hall is represented in _fig._ 126.; _a_ is the upper part of the condenser to which steam is admitted from the slide after having worked the piston; _k_ is the section of a thin plate, forming the top of the condenser, perforated with small holes, in which the tubes are inserted so as to be steam-tight and water-tight. Water is admitted to flow around these tubes between the top _k_ and the bottom _d_ of the condenser, so as to keep them constantly at a low temperature. The steam passes from _a_ through the tubes to the lower chamber _f_ of the condenser, where it is reduced to water by the cold to which it has been exposed. A supply of cold water is constantly pumped through the condenser, so as to keep the tubes at a low temperature. The air-pump _g_ is of the usual construction, having valves in the piston opening upwards, and [Pg460] similar valves in the cover of the pump also opening upwards. The water formed by the condensed steam in _f_ is drawn through the foot-valve, and after passing through the piston-valves, is discharged by the up-stroke of the piston into the hot well. Any air, or other permanent gas, which may be admitted by leakage through the tubes of the condenser, or by any other means, is likewise drawn out by this pump, and when drawn into the hot well is carried from thence to the feeding apparatus of the boiler, to which it is transferred by the feed-pump.

[Illustration: _Fig._ 126.]

A provision is likewise made by which the steam escaping at the safety-valve is condensed and carried away to the feeding cistern.

(214.) One of the remedies proposed for the evil consequences arising from incrustation is the substitution of copper for iron boilers. The attraction which produces the adhesion of the calcareous matter held in solution by salt water to the surface of iron has no existence in copper, and all the saline and other alkaline matter precipitated in the boiling water in [Pg461] copper boilers is suspended in a loose form, and carried off by the process of blowing out.

Besides the injury arising from the deposition of salt and the incrustation on the inner surface of boilers, an evil of a formidable kind attends the accumulation of soot mixed with salt in the flues, which proceeds from the leaks. In the seams of the boiler there are numerous apertures, of dimensions so small as to be incapable of being rendered stanch by any practicable means, through which the water within the boiler filters, and the salt which it carries with it mixes with the soot, forming a compound which rapidly corrodes the boilers. This process of corrosion in the flues takes place not less in copper than in iron boilers. In cleansing the flues of a copper boiler, the salt and soot which was thrown out upon the iron-plates which formed the flooring of the engine-room, having remained there for some time, left behind it a permanent appearance of copper on the iron flooring, arising from the precipitation of the copper which had combined with the soot and salt in the flues.[36] In this case the leaks from whence the salt proceeded were found, on careful examination, so unimportant, that the usual means to stanch them could not be resorted to without the risk of increasing the evil.

(215.) In the application of the steam-engine to the propulsion of vessels in voyages of great extent, the economy of fuel acquires an importance greater than that which appertains to it in land-engines, even in localities the most removed from coal-mines, and where its expense is greatest. The practical limit to steam-voyages being determined by the greatest quantity of coals which a steam-vessel can carry, every expedient by which the efficiency of the fuel can be increased becomes a means, not merely of a saving of expense, but of an increased extension of steam-power to navigation. Much attention has been bestowed on the augmentation of the duty of engines in the mining districts of Cornwall, where the question of their efficiency is merely a question of economy, but far greater care should be given to this subject when the practicability of maintaining intercourse by steam between distant points of the globe will perhaps depend on the effect produced by a given quantity [Pg462] of fuel. So long as steam-navigation was confined to river and channel transport, and to coasting voyages, the speed of the vessel was a paramount consideration, at whatever expenditure of fuel it might be obtained; but since steam-navigation has been extended to ocean-voyages, where coals must be transported sufficient to keep the engine in operation for a long period of time without a fresh relay, greater attention has been bestowed upon the means of economising it.

Much of the efficiency of fuel must depend on the management of the fires, and therefore on the skill and care of the stokers. Formerly the efficiency of firemen was determined by the abundant production of steam, and so long as the steam was evolved in superabundance, however it might have blown off to waste, the duty of the stoker was considered as well performed. The regulation of the fires according to the demands of the engine were not thought of, and whether much or little steam was wanted, the duty of the stoker was to urge the fires to their extreme limit.

Since the resistance opposed by the action of the paddle-wheels of a steam-vessel varies with the state of the weather, the consumption of steam in the cylinders must undergo a corresponding variation; and if the production of steam in the boilers be not proportioned to this, the engines will either work with less efficiency than they might do under the actual circumstances of the weather, or more steam will be produced in the boilers than the cylinders can consume, and the surplus will be discharged to waste through the safety-valves. The stokers of a marine engine, therefore, to perform their duty with efficiency, and obtain from the fuel the greatest possible effect, must discharge the functions of a self-regulating furnace, such as has been already described: they must regulate the force of the fires by the amount of steam which the cylinders are capable of consuming, and they must take care that no unconsumed fuel is allowed to be carried away from the ash-pit.

(216.) Until within a few years of the present time the heat radiated from every part of the surface of the boiler was allowed to go to waste, and to produce injurious effects on those parts of the vessel to which it was transmitted. This evil, [Pg463] however, has been lately removed by coating the boilers, steam-pipes, &c. of steam-vessels with felt, by which the escape of heat from the surface of the boiler is very nearly, if not altogether, prevented. This felt is attached to the boiler-surface by a thick covering of white and red lead. This expedient was first applied in the year 1818 to a private steam-vessel of Mr. Watt's called the _Caledonia_, and it was subsequently adopted in another vessel, the machinery of which was constructed at Soho, called the _James Watt_.

The economy of fuel depends in a considerable degree on the arrangement of the furnaces, and the method of feeding them. In general each boiler is worked by two or more furnaces communicating with the same system of flues. While the furnace is fed, the door being open, a stream of cold air rushes in, passing over the burning fuel and lowering the temperature of the flues: this is an evil to be avoided. But, on the other hand, if the furnaces be fed at distant intervals, then each furnace will be unduly heaped with fuel, a great quantity of smoke will be evolved, and the combustion of the fuel will be proportionally imperfect. The process of coking in front of the grate, which would insure a complete combustion of the fuel, has been already described (147.). A frequent supply of coals, however, laid carefully on the front part of the grate, and gradually pushed backwards as each fresh feed is introduced, would require the fire-door to be frequently opened, and cold air to be admitted. It would also require greater vigilance on the part of the stokers than can generally be obtained in the circumstances in which they work. In steam-vessels the furnaces are therefore fed less frequently, fuel introduced in greater quantities, and a less perfect combustion produced.

When several furnaces are constructed under the same boiler, communicating with the same system of flues, the process of feeding, and consequently opening one of them, obstructs the due operation of the others, for the current of cold air which is thus admitted into the flues checks the draft and diminishes the efficiency of the furnaces in operation. It was formerly the practice in vessels exceeding one hundred horse-power, to place four furnaces under each boiler, communicating with the same system of flues. Such an arrangement [Pg464] was found to be attended with a bad draft in the furnaces, and therefore to require a greater quantity of heating surface to produce the necessary evaporation. This entailed upon the machinery the occupation of more space in the vessel in proportion to its power; it has therefore been more recently the practice to give a separate system of flues to each pair of furnaces, or, at most, to every three furnaces. When three furnaces communicate with a common flue, two will always be in operation, while the third is being cleared out; but if the same quantity of fire were divided among two furnaces, then the clearing out of one would throw out of operation half the entire quantity of fire, and during the process the evaporation would be injuriously diminished. It is found by experience, that the side plates of furnaces are liable to more rapid destruction than their roofs, owing, probably, to a greater liability to deposit. Furnaces, therefore, should not be made narrower than a certain limit. Great depth from front to back is also attended with practical inconvenience, as it renders firing tools of considerable length, and a corresponding extent of stoking room necessary. It is recommended, by those who have had much practical experience in steam-vessels, that furnaces six feet in depth from front to back should not be less than three feet in width, to afford means of firing with as little injury to the side plates as possible, and of keeping the fires in the condition necessary for the production of the greatest effect. The tops of the furnaces almost never decay, and seldom are subject to an alteration of figure, unless the level of the water be allowed to fall below them.[37]

(217.) A form of marine engine was some years since proposed and patented by Mr. Thomas Howard, possessing much novelty and ingenuity, and having pretensions to a very extraordinary economy of fuel, in addition to the advantages claimed by Mr. Hall. In Mr. Howard's engines, the steam, as in Mr. Hall's, is constantly reproduced from the same water, so that pure or distilled water may be used; but Mr. Howard dispenses altogether with the use of a boiler.

A quantity of mercury is placed in a shallow wrought-iron vessel over a coke fire, by which it is maintained at a [Pg465] temperature varying from 400° to 500°. The surface exposed to the fire was computed at three fourths of a square foot for each horse-power. The upper surface of the mercury was covered by a very thin plate of iron in contact with it, and so contrived as to present about four times as much surface as that exposed beneath the fire. Adjacent to this a vessel of water was placed, maintained nearly at the boiling point, and communicating by a nozzle and valve with the chamber immediately above the mercury. At intervals corresponding to the motion of the piston a small quantity of water was injected from this vessel, and thrown upon the plate of iron resting upon the hot mercury. From this it received not only the heat necessary to convert it into common steam, but to give it the qualities of highly superheated steam. In fact, the steam thus produced had a temperature considerably above that which corresponded to its pressure, and was, therefore, capable of being deprived of more or less of its heat without being condensed. (94.) The quantity of water injected into the steam-chamber was regulated by the power at which the engine was intended to be worked. The fire was supplied with air by a blower subject to exact regulation. The steam thus produced was conducted to a chamber surrounding the working cylinder, and this chamber itself was enclosed by another space through which the air from the furnace passed before it reached the flue. By this contrivance the air imparted its redundant heat to the steam, as the latter passed to the cylinder, and raised its temperature to about 400°, the pressure, however, not exceeding 25 lbs. per square inch. The valves, governing the admission of steam to the piston, were adapted for expansive action.

The vacuum on the opposite side was maintained by condensation in the following manner:—The condenser was a copper vessel placed in a cistern of cold water, and the steam was admitted to it from the cylinder by an eduction pipe in the usual way. A jet was introduced from an adjacent vessel filled with distilled water, and the condensing water and condensed steam were pumped from the condenser as in common engines. The warm water thus pumped out of the [Pg466] condenser was drawn through a copper worm, carried with many coils through a cistern of cold water, so that when it arrived at the end of this pipe it was reduced nearly to the temperature of the atmosphere. The pipe was thus brought to the vessel of distilled water already mentioned, and the water supplied by it replaced. The water admitted to the condenser through the condensing jet being purged of air, a small air-pump was sufficient, since it had only to exhaust the condenser and tubes at starting, and to remove the air which might be admitted by leakage. Mr. Howard stated that the condensation took place as rapidly and perfectly as in the best engines of the common kind.

An engine of this construction was in the spring of 1835 placed in the government steamer called the _Comet_. It was stated, that though the machinery was not advantageously constructed, a part of the engine being old, and not made expressly for a boiler of this kind, the vessel performed a voyage from Falmouth to Lisbon, in which the consumption of fuel did not exceed a third of her former consumption when worked by Boulton and Watt's engines, the former consumption of coals being about eight hundred pounds per hour, and the consumption of Mr. Howard's engine being less than two hundred and fifty pounds of coke per hour.

The advantages claimed for this contrivance were the following: _first_, the small space and weight occupied by the machinery, arising from the absence of a boiler; _second_, the diminished consumption of fuel; _third_, the reduced size of the flues; _fourth_, the removal of the injurious effects arising from deposit and incrustation; _fifth_, the absence of smoke.

(218.) The method by which the greatest quantity of practical effect can be obtained from a given quantity of fuel must, however, mainly depend on the extended application of the expansive principle. This has been the means by which an extraordinary amount of duty has been obtained from the Cornish engines. The difficulty of the application of this principle in marine engines has arisen from the objections entertained in Europe to the use of steam of high pressure under the circumstances in which the engine must be worked at sea. To apply the expansive principle, it is necessary that the moving power at the commencement of the stroke shall considerably exceed the [Pg467] resistance, its force being gradually attenuated till the completion of the stroke, when it will at length become less than the resistance. This condition may, however, be attained with steam of limited pressure, if the engine be constructed with a sufficient quantity of piston-surface. This method of rendering the expansive principle available at sea, and compatible with low-pressure steam, has recently been brought into operation by Messrs. Maudslay and Field. Their improvement consists in adapting two steam-cylinders in one engine, in such a manner that the steam shall act simultaneously on both pistons, causing them to ascend and descend together. The piston-rods are both attached to the same horizontal cross-head, whereby their combined action is applied to one crank by means of a connecting rod placed between the pistons.

[Illustration: _Fig._ 127.]

A section of such an engine, made by a plane passing through the two piston-rods P P′ and cylinders, is represented in _fig._ 127. The piston-rods are attached to a cross-head C, [Pg468] which ascends and descends with them. This cross-head drives upwards and downwards an axle D, to which the lower end of the connecting rod E is attached. The other end of the connecting rod drives the crank-pin F, and imparts revolution to the paddle-shaft G. A rod H conveys motion by means of a beam I to the rod K of the air-pump E.

(219.) Connected with this, and in the same patent, another improvement is included, consisting of the application of a hollow wrought-iron framing carried across the vessel above the machinery, to support the whole of the bearings of the crank-shaft. A plan of this, including the cylinders and paddle-wheel, is represented in _fig._ 128. The advantages proposed by these improvements are simplicity of construction, more direct action on the crank, economy of space and weight of material, combined with increased area of the piston, whereby a given evaporating power of the boiler is rendered productive, by extended application of the expansive principle, of a greater moving power than in former arrangements. Consequently, under like circumstances, greater power and economy of fuel is obtained, with the further advantage at sea, that when the engine is reduced in its speed, either by the vessel being deeply laden with coal, as is the case at the commencement of a long sea voyage, or by head winds, more steam may be given to the cylinders, and consequently more speed imparted to the vessel, all the steam produced in the boiler being usefully employed.

(220.) Another improvement, having the same objects, and analogous to the preceding, has been likewise patented by Messrs. Maudslay and Field. This consists in the adoption of a cylinder of greater diameter, having two piston-rods P P′, as represented in _fig._ 129., of considerable length, connected at the top by a cross-head C. From this cross-head is carried downwards the connecting rod D, which drives the crank-pin E, and thereby works the paddle-shaft S. In this case the paddle-shaft is extended immediately above the piston, and the double piston-rod has sufficient length to be above the paddle-shaft when the piston is at the bottom of its stroke. This improvement is intended to be applied more

## particularly for engines for river navigation, the advantages

resulting from [Pg469] it being that a paddle-shaft placed at a given height from the bottom of the vessel will be enabled to receive a longer stroke of piston than by any other arrangement now in use. A more [Pg470] compact and firm connection of the cylinder with the crank-shaft bearings is effected by it, and a cylinder of much greater diameter may be applied by which the expansive action of steam may be more fully brought into play; and a more direct action of the steam-power on the crank with a less weight of materials and a greater economy of space may be obtained than by any of the arrangements of marine engines hitherto used.

[Illustration: _Fig._ 128.]

[Illustration: _Fig._ 129.]

(221.) Mr. Francis Humphrys has obtained a patent for a form of marine engine, by which some simplification of the machinery is attained, and the same power comprised within more limited dimensions. In this engine there is attached to the piston of the cylinder, instead of a piston-rod, a hollow casing D D (_fig._ 130.), which moves through a stuffing-box G, constructed in a manner similar to the stuffing-box of a piston-rod. In the figure, this casing is presented in section, but [Pg471] its form is that of a long narrow slit, or opening, rounded at either end as exhibited in the plan (_fig._ 131) of the cylinder-cover. The crank C is driven by the other end of the connecting rod H, the crank-shaft being immediately above the centre of the piston and the connecting rod passing through the oblong opening D, and descending into the hollow piston-rod it is attached to an axis I at the bottom of the piston. A box or cover K K encloses the cross-piece or axis I with its bearings, and is [Pg472] attached so as to be steam-tight to the bottom of the piston. A hollow space L L is cast in the bottom of the cylinder for the reception of the box K K, when the piston is at the bottom of the cylinder.

[Illustration: _Fig._ 130.]

[Illustration: _Fig._ 131.]

By this arrangement the force by which the piston is driven in its ascent and descent is communicated to the connecting rod, not, as usual, through the intervention of a piston-rod, but directly from the piston itself by the cross-pin I, and from thence to the crank C, which it drives without the intervention of beams, cross-heads, or any similar appendage.

The slide-valves regulating the admission and eduction of steam are represented at _a_; the rod of the air-pump is shown at _d_, being worked by a crank placed on the centre of the great crank shaft.[38]

(222.) To obtain from the moving power its full amount of mechanical effect in propelling the vessel, it would be necessary that its force should propel, by constantly acting against the water in a horizontal direction, and with a motion contrary to the course of the vessel. No system of mechanical propellers has, however, yet been contrived capable of perfectly accomplishing this. Patents have been granted for many ingenious mechanical combinations to impart to the propelling surfaces such angles as appeared to the respective contrivers most advantageous. In most of these the mechanical complexity has formed a fatal objection. No part of the machinery of a steam-vessel is so liable to become deranged at sea as the paddle-wheels; and, therefore, that simplicity of construction which is compatible with those repairs which are possible on such emergencies is quite essential for safe practical use.

[Illustration: _Fig._ 132.]

The ordinary paddle-wheel, as has been already stated, is a wheel revolving upon a shaft driven by the engine, and carrying upon its circumference a number of flat boards, called paddle-boards, which are secured by nuts and braces in a fixed position; and that position is such that the planes [Pg473] of the paddle-boards diverge nearly from the centre of the shaft on which the wheel turns. The consequence of this arrangement is that each paddle-board can only act in that direction which is most advantageous for the propulsion of the vessel when it arrives near the lowest point of the wheel. In _fig._ 132. let O be the shaft on which the common paddle-wheel revolves; the position of the paddle-boards are represented at A, B, C, &c.; X, Y represents the water line, the course of the vessel being supposed to be from X to Y; the arrows represent the direction in which the paddle-wheel revolves. The wheel is immersed to the depth of the lowest paddle-board, since a less degree of immersion would render a portion of the surface of each paddle-board mechanically useless. In the position A the whole force of the paddle-board is efficient for propelling the vessel; but as the paddle enters the water in the position H, its action upon the water, not being horizontal, is only partially effective for propulsion: a part of the force which drives the paddle is expended in depressing the water, and the remainder in driving it contrary to the course of the vessel, and, therefore, by its re-action producing a certain propelling effect. The tendency, however, of the paddle entering the water at H, is to form a hollow or trough, which the water, by its ordinary property, has a continual tendency to fill up. After passing the lowest point A, as the paddle approaches the position B, where it [Pg474] emerges from the water, its action again becomes oblique, a part only having a propelling effect, and the remainder having a tendency to raise the water, and throw up a wave and spray behind the paddle-wheel. It is evident that the more deeply the paddle-wheel becomes immersed, the greater will be the proportion of the propelling power thus wasted in elevating and depressing the water; and if the wheel were immersed to its axis, the whole force of the paddle-boards, on entering and leaving the water, would be lost, no part of it having a tendency to propel. If a still deeper immersion take place, the paddle-boards above the axis would have a tendency to retard the course of the vessel. When the vessel is, therefore, in proper trim, the immersion should not exceed nor fall short of the depth of the lowest paddle; but for various reasons it is impossible in practice to maintain this fixed immersion: the agitation of the surface of the sea, causing the vessel to roll, will necessarily produce a great variation in the immersion of the paddle-wheels, one becoming frequently immersed to its axle, while the other is raised altogether out of the water. Also the draught of water of the vessel is liable to change, by the variation in her cargo; this will necessarily happen in steamers which take long voyages. At starting they are heavily laden with fuel, which as they proceed is gradually consumed, whereby the vessel is lightened.

(223.) To remove this defect, and economise as much as possible the propelling effect of the paddle-boards, it would be necessary so to construct them that they may enter and leave the water edgeways, or as nearly so as possible; such an arrangement would be, in effect, equivalent to the process called feathering, as applied to oars. Any mechanism which would perfectly accomplish this would cause the paddles to work in almost perfect silence, and would very nearly remove the inconvenient and injurious vibration which is produced by the action of the common paddles. But the construction of feathering paddles is attended with great difficulty, under the peculiar circumstances in which such wheels work. Any mechanism so complex that it could not be easily repaired when deranged, with such engineering implements and skill [Pg475] as can be obtained at sea, would be attended with great objections; and the efficiency of its propelling action would not compensate for the dangers which must attend upon the helpless state of a steamer, deprived of her propelling agents.

Feathering paddle-boards must necessarily have a motion independently of the motion of the wheel, since any fixed position which could be given to them, though it might be most favourable to their action in one position would not be so in their whole course through the water. Thus the paddle-board when at the lowest point should be in a vertical position, or so placed that its plane, if continued upwards, would pass through the axis of the wheel. In other positions, however, as it passes through the water, it should present its upper edge, not towards the axle of the wheel, but towards a point above the highest point of the wheel. The precise point to which the edge of the paddle-board should be directed is capable of mathematical determination. But it will vary according to circumstances, which depend on the motion of the vessel. The progressive motion of the vessel, independently of the wind or current, must obviously be slower than the motion of the paddle-boards round the axle of the wheel; since it is by the difference of these velocities that the re-action of the water is produced by which the vessel is propelled. The proportion, however, between the progressive speed of the vessel and the rotative speed of the paddle-boards is not fixed: it will vary with the shape and structure of the vessel, and with its depth of immersion; nevertheless it is upon this proportion that the manner in which the paddle-boards should shift their position must be determined. If the progressive speed of the vessel were nearly equal to the rotative speed of the paddle-boards, the latter should so shift their position that their upper edges should be presented to a point very little above the highest point of the wheel. This is a state of things which could only take place in the case of a steamer of a small draught of water, shallop-shaped, and so constructed as to suffer little resistance from the fluid. On the other hand, the greater the depth of immersion, and the less fine the lines of the [Pg476] vessel, the greater will be the resistance in passing through the water, and the greater will be the proportion which the rotative speed of the paddle-boards will bear to the progressive speed of the vessel. In this latter case the independent motion of the paddle-boards should be such that their edges, while in the water, shall be presented towards a point considerably above the highest point of the paddle-wheel.

A vast number of ingenious mechanical contrivances have been invented and patented for accomplishing the object just explained. Some of these have failed from the circumstance of their inventors not clearly understanding what precise motion it was necessary to impart to the paddle-board: others have failed from the complexity of the mechanism by which the desired effect was produced.

(224.) In the year 1829 a patent was granted to Elijah Galloway for a paddle-wheel with movable paddles, which patent was purchased by Mr. William Morgan, who made various alterations in the mechanism, not very materially departing from the principle of the invention.

[Illustration: _Fig._ 133.]

This paddle-wheel is represented in _fig._ 133. The contrivance may be shortly stated to consist in causing the wheel which bears the paddles to revolve on one centre, and the radial arms which move the paddles to revolve on another centre. Let A B C D E F G H I K L be the polygonal circumference of the paddle-wheel, formed of straight bars, securely connected together at the extremities of the spokes or radii of the wheel which turns on the shaft which is worked by the engine; the centre of this wheel being at O. So far this wheel is similar to the common paddle-wheel; but the paddle-boards are not, as in the common wheel, fixed at A B C, &c., so as to be always directed to the centre O, but are so placed that they are capable of turning on axles which are always horizontal, so that they can take any angle with respect to the water which may be given to them. From the centres, or the line joining the pivots on which these paddle-boards turn, there proceed short arms K, firmly fixed to the paddle-boards at an angle of about 120°. On a motion given to this arm K, it will therefore give a corresponding angular motion to the paddle-board, so as to make it turn on its pivots. At [Pg477] the extremities of the several arms marked K is a pin or pivot, to which the extremities of the radial arms L are severally attached, so that the angle between each radial arm L and the short paddle-arm K is capable of being changed by any motion imparted to L; the radial arms are connected at the other end with a centre, round which they are capable of revolving. Now, since the points A B C, &c., which are the pivots on which the paddle-boards turn, are moved in the circumference of a circle, of which the centre is O, they are always at the same distance from that point; consequently they will continually vary their distance from the other centre P. Thus, when a paddle-board arrives at that point of its revolution at which the centre round which it revolves lies precisely between it and the centre O, its distance from the former centre is less than in any other position. As it departs from that point, its distance from that centre gradually increases until it arrives at the opposite point of its revolution, where the centre O is exactly between it and the former centre; then the distance of the paddle-board from the former centre is greatest. [Pg478] This constant change of distance between each paddle-board and the centre P is accommodated by the variation of the angle between the radial arm L and the short paddle-board arm K; as the paddle-board approaches the centre P this gradually diminishes; and as the distance of the paddle-board increases, the angle is likewise augmented. This change in the magnitude of the angle, which thus accommodates the varying position of the paddle-board with respect to the centre P, will be observed in the figure. The paddle-board D is nearest to P; and it will be observed that the angle contained between L and K is there very acute; at E the angle between L and K increases, but is still acute; at G it increases to a right angle; at H it becomes obtuse; and at K, where it is most distant from the centre P, it becomes most obtuse. It again diminishes at K, and becomes a right angle between A and B. Now this continual shifting of the direction of the short arm K is necessarily accompanied by an equivalent change of position in the paddle-board to which it is attached; and the position of the second centre P is, or may be, so adjusted that this paddle-board, as it enters the water and emerges from it, shall be such as shall be most advantageous for propelling the vessel, and therefore attended with less of that vibration which arises chiefly from the alternate depression and elevation of the water, owing to the oblique action of the paddle-boards.

(225.) In the year 1833, Mr. Field, of the firm of Maudslay and Field, constructed a paddle-wheel with fixed paddle-boards, but each board being divided into several narrow slips arranged one a little behind the other, as represented in _fig._ 134. These divided boards he proposed to arrange in such cycloidal curves that they must all enter the water at the same place in immediate succession, avoiding the shock produced by the entrance of the common board. These split paddle-boards are as efficient in propelling when at the lowest point as the common paddle-boards, and when they emerge the water escapes simultaneously from each narrow board, and is not thrown up, as is the case with common paddle-boards.[39]

[Illustration: _Fig._ 134.]

[Pg479] The theoretical effect of this wheel is the same as that of the common wheel, and experience alone, the result of which has not yet been obtained, can prove its efficiency. The number of bars, or separate parts into which each paddle-board is divided, has been very various. When first introduced by Mr. Galloway each board was divided into six or seven parts: this was subsequently reduced, and in the more recent wheels of this form constructed for the government vessels the paddle-boards consist only of two parts, coming as near to the common wheel as is possible, without altogether abandoning the principle of the split paddle.

(226.) To obtain an approximate estimate of the extent to which steam-power is applicable to long sea-voyages, it would be necessary to investigate the mutual relation which, in the existing state of this application of steam-power, exists between the capacity or tonnage of the vessel, the magnitude, weight, and power, of the machinery, the available stowage for fuel, and the average speed attainable in all [Pg480] weathers, as well as the general purposes to which the vessel is to be appropriated, whether for the transport of goods or merchandise, or merely for despatches and passengers, or for both of these combined. That portion of the capacity of the vessel which is appropriated to the moving power consists of the space occupied by the machinery and the fuel. The distribution of it between these must mainly depend on the length of the voyage which the vessel must make without receiving a fresh supply of coals. If the trips be short, and frequent relays of fuel can be obtained, then the space allotted to the machinery may bear a greater proportion to that assigned to the fuel; but in proportion as each uninterrupted stage of the voyage is increased, a greater stock of coals will be necessary, and a proportionally less space left for the machinery. Other things being the same, therefore, steam-vessels intended for long sea-voyages must be less powerful in proportion to their tonnage.

It will be apparent that every improvement which takes place in the application of the steam-engine to navigation will modify all these data on which such an investigation must depend. Every increased efficiency of fuel, from whatever cause it may be derived, will either increase the useful tonnage of the vessel, or increase the length of the voyage of which it is capable. Various improvements have been and are still in progress, by which this efficiency has undergone continual augmentation, and voyages may now be accomplished with moderate economy and profit, to which a few years since marine engines could not be applied with permanent advantage. The average speed of steam-vessels has also undergone a gradual increase by such improvements. During the four years ending June, 1834, it was found that the average rate of steaming obtained from fifty-one voyages made by the Admiralty steamers between Falmouth and Corfu, exclusive of stoppages, was seven miles and a quarter an hour direct distance between port and port. The vessels which performed this voyage varied from 350 to 700 tons measured burden, and were provided with engines varying from 100 to 200 horse-power, with stowage for coals varying from 80 to 240 tons. The proportion of the power to the [Pg481] tonnage varied from one horse to three tons to one horse to four tons. Thus the MESSENGER had a power of 200 horses and measured 730 tons; the FLAMER had a power of 120 horses, and measured 500 tons; the COLUMBIA had a power of 120 horses, and measured 360 tons. In general it may be assumed that for the shortest class of trips, such as those of the Channel steamers, the proportion of the power to the tonnage should be about one horse for every two tons; but for the longer class of voyages, the proportion of power to tonnage should be about one horse-power to from three to four tons measured tonnage. These data, however, must be received as very rough approximations, subject to considerable modifications in their application to particular vessels. We have already stated that the nominal horse-power is itself extremely indefinite; and if, as is now customary in the longer class of voyages, the steam be worked expansively, then the nominal power almost ceases to have any definite relation to the actual performance of the vessel. It is usual to calculate the horse-power by assuming a uniform pressure of steam upon the piston, and, consequently, by excluding the consideration of the effect of expansion. The most certain test of the amount of mechanical power exerted by the machinery would be obtained from the quantity of water actually transmitted in the form of steam from the boiler to the cylinder. But the effect of this would also be influenced by the extent to which the expansive principle has been brought into operation.

From the reported performances of the larger class of steam-ships within the last few years, it would appear that the average speed has been increased since the estimate above mentioned, which was obtained in 1834; and on comparing the consumption of fuel with the actual performance, it would appear that the efficiency of fuel has also been considerably augmented. No extensive course of accurate experiments or observations have, however, been obtained from which correct inferences may be drawn of the probable limits to which steam-navigation, in its present state, is capable of being extended. The jealousy of rival companies has obstructed the inquiries of those who, solicitous more [Pg482] for the general advancement of the art than for the success of individual enterprises, have directed their attention to this question; and it is hardly to be expected that sufficiently correct and extensive data can be obtained for this purpose.

(227.) Increased facility in the extension and application of steam-navigation is expected to arise from the substitution of iron for wood, in the construction of vessels. Hitherto iron steamers have been chiefly confined to river-navigation; but there appears no sufficient reason why their use should be thus limited. For sea-voyages they offer many advantages; they are not half the weight of vessels of equal tonnage constructed of wood; and, consequently, with the same tonnage they will have less draught of water, and therefore less resistance to the propelling power; or, with the same draught of water and the same resistance, they will carry a proportionally heavier cargo. The nature of their material renders them more stiff and unyielding than timber; and they do not suffer that effect which is called _hogging_, which arises from a slight alteration which takes place in the figure of a timber vessel in rolling, accompanied by an alternate opening and closing of the seams. Iron vessels have the further advantage of being more proof against fracture upon rocks. If a timber vessel strike, a plank is broken, and a chasm opened in her many times greater than the point of rock which produces the concussion. If an iron vessel strike, she will either merely receive a dinge, or be pierced by a hole equal in size to the point of rock which she encounters. Some examples of the strength of iron vessels were given by Mr. Macgregor Laird, in his evidence before the Committee of the Commons on Steam Navigation, among which the following may be mentioned:—An iron vessel, called the ALBURKAH, in one of their experimental trials got aground, and lay upon her anchor: in a wooden vessel the anchor would probably have pierced her bottom; in this case, however, the bottom was only dinged. An iron vessel, built for the Irish Inland Navigation Company, was being towed across Lough Derg in a gale of wind, when the towing rope broke, and she was driven upon rocks, on which she bumped for a considerable time [Pg483] without any injury. A wooden vessel would in this case have gone to pieces. A further advantage of iron vessels (which in warm climates is deserving of consideration) is their greater coolness and perfect freedom from vermin.

Iron steam-vessels on a very large scale are now in preparation in the ports of Liverpool and Bristol, intended for long sea-voyages. The largest vessel of this description which has yet been projected is stated to be in preparation for the voyage between Bristol and New York, by the company who have established the steam-ship called the Great Western, plying between these places.

Several projects for the extension of steam-navigation to voyages of considerable length have lately been entertained both by the public and by the legislature, and have imparted to every attempt to improve steam-navigation increased interest. A committee of the House of Commons collected evidence and made a report in the last session in favour of an experiment to establish a line of steam-communication between Great Britain and India. Two routes have been suggested by the committee, each being a continuation of the line of Admiralty steam-packets already established to Malta and the Ionian Isles. One of the routes proposed is through Egypt, the Red Sea, and across the Indian Ocean to Bombay, or some of the other presidencies; the other across the north part of Syria to the banks of the Euphrates, by that river to the Persian Gulf, and from thence to Bombay. Each of these routes will be attended with peculiar difficulties, and in both a long sea-voyage will be encountered.

In the route by the Red Sea it is proposed to establish steamers between Malta and Alexandria (eight hundred and sixty miles). A steamer of four hundred tons' burden and one hundred horse-power would perform this voyage, upon an average of all weathers incident to the situation, in from five to six days, consuming ten tons of coal per day. But it is probable that it might be found more advantageous to establish a higher ratio between the power and the tonnage. From Alexandria the transit might be effected by land across the isthmus to Suez—a journey of from four to five days—by caravan and camels; or the transit might be made either [Pg484] by land or water from Alexandria to Cairo, a distance of one hundred and seventy-three miles; and from Cairo to Suez, ninety-three miles, across the desert, in about five days. At Suez would be a station for steamers, and the Red Sea would be traversed in three runs or more. If necessary, stations for coals might be established at Cosseir, Judda, Mocha, and finally at Aden or at Socatra—an island immediately beyond the mouth of the Red Sea, in the Indian Ocean; the run from Suez to Cosseir would be three hundred miles—somewhat more than twice the distance from Liverpool to Dublin. From Cosseir to Judda, four hundred and fifty miles; from Judda to Mocha, five hundred and seventeen miles; and from Mocha to Socatra, six hundred and thirty-two miles. It is evident that all this would, without difficulty, in the most unfavourable weather, fall within the present powers of steam-navigation. If the terminus of the passage be Bombay, the run from Socatra to Bombay will be twelve hundred miles, which would be from six to eight days' steaming. The whole passage from Alexandria to Bombay, allowing three days for delay between Suez and Bombay, would be twenty-six days: the time from Bombay to Malta would therefore be about thirty-three days; and adding fourteen days to this for the transit from Malta to England, we should have a total of forty-seven days from London to Bombay, or about seven weeks.

If the terminus proposed were Calcutta, the course from Socatra would be one thousand two hundred and fifty miles south-east to the Maldives, where a station for coals would be established. This distance would be equal to that from Socatra to Bombay. From the Maldives, a run of four hundred miles would reach the southern point of Ceylon, called the Point de Galle, which is the best harbour (Bombay excepted) in British India: from the Point de Galle, a run of six hundred miles will reach Madras, and from Madras to Calcutta would be a run of about six hundred miles. The voyage from London to Calcutta would be performed in about sixty days.

At a certain season of the year there exists a powerful physical opponent to the transit from India to Suez: from [Pg485] the middle of June until the end of September, the south-west monsoon blows with unabated force across the Indian Ocean, and more

## particularly between Socatra and Bombay. This wind is so violent

as to leave it barely possible for the most powerful steam-packet to make head against it, and the voyage could not be accomplished without serious wear and tear upon the vessels during these months.

The attention of parliament has therefore been directed to another line of communication, not liable to this difficulty: it is proposed to establish a line of steamers from Bombay through the Persian Gulf to the Euphrates.

The run from Bombay to a place called Muscat, on the southern shore of the gulf, would be eight hundred and forty miles in a north-west direction, and therefore not opposed to the south-west monsoon. From Muscat to Bassidore, a point upon the northern coast of the strait at the mouth of the Persian Gulf, would be a run of two hundred and fifty-five miles; from Bassidore to Bushire, another point on the eastern coast of the Persian Gulf, would be a run of three hundred miles; and from Bushire to the mouth of the Euphrates, would be one hundred and twenty miles. It is evident that the longest of these runs would offer no more difficulty than the passage from Malta to Alexandria. From Bussora, near the mouth of the Euphrates, to Bir, a town upon its left bank near Aleppo, would be one thousand one hundred and forty-three miles, throughout which there are no physical obstacles to the river-navigation which may not be overcome. Some difficulties arise from the wild and savage character of the tribes who occupy its banks. It is, however, thought that by proper measures, and securing the co-operation of the pacha of Egypt, any serious obstruction from this cause may be removed. From Bir, by Aleppo, to Scanderoon, a port upon the Mediterranean, opposite Cyprus, is a land-journey, said to be attended with some difficulty, but not of great length; and from Scanderoon to Malta is about the same distance as between the latter place and Alexandria. It is calculated that the time from London to Bombay by the Euphrates—supposing the passage to be successfully [Pg486] established—would be a few days shorter than by Egypt and the Red Sea.

Whichever of these courses may be adopted, it is clear that the difficulties, so far as the powers of the steam engine are concerned, lie in the one case between Socatra and Bombay, or between Socatra and the Maldives, and in the other case between Bombay and Muscat. This, however, has already been encountered and overcome on four several voyages by the HUGH LINDSAY steamer from Bombay to Suez: that vessel encountered a still longer run on these several trips, by going, not to Socatra, but to Aden, a point on the coast of Arabia, near the Straits of Babel Mandeb, being a run of one thousand six hundred and forty-one miles, which she performed in ten days and nineteen hours. The same trip has since been repeatedly made by other steamers; and, in the present improved state of steam navigation, no insurmountable obstacles are opposed to their passage.

[Illustration]

FOOTNOTES:

[35] This cut is taken from the plate of the engine of the Red Rover, manufactured by Boulton and Watt, given in the last edition of _Tredgold on the Steam Engine_.

[36] Appendix I., _on Marine Boilers, by J. Dinnen; Tredgold_ _on the Steam Engine_, second edition.

[37] _Tredgold on the Steam Engine_, Appendix, I. p. 171.

[38] Engines on a very large scale constructed upon this principle are said to be in process of construction for an iron steam-vessel of great tonnage, which is in preparation for the New York passage. It is said that the cylinders of these engines will be one hundred and twenty inches in diameter.

[39] A patent was subsequently taken out for these by Mr. Galloway. Mr. Field did not persevere in its use at the time he invented it. It has, however, been more generally adopted since the date of Galloway's patent.

[Pg487]

[Illustration]

CHAP. XIV.

AMERICAN STEAM NAVIGATION.

STEAM NAVIGATION FIRST ESTABLISHED IN AMERICA. — CIRCUMSTANCES WHICH LED TO IT. — FITCH AND RUMSEY. — STEVENS OF HOBOKEN. — LIVINGSTONE AND FULTON. — EXPERIMENTS ON THE SEINE. — FULTON'S FIRST BOAT. — THE HUDSON NAVIGATED BY STEAM. — EXTENSION AND IMPROVEMENT OF RIVER NAVIGATION. — SPEED OF AMERICAN STEAMERS. — DIFFERENCE BETWEEN THEM AND EUROPEAN STEAMERS. — SEA-GOING AMERICAN STEAMERS. — AMERICAN PADDLE-WHEELS. — LAKE STEAMERS. — THE MISSISIPPI AND ITS TRIBUTARIES. — STEAMERS NAVIGATING IT. — THEIR STRUCTURE AND MACHINERY. — NEW ORLEANS HARBOUR. — STEAM TUGS.

(228.) The credit of having afforded the first practical solution of the problem to apply the steam engine to the propulsion of ships, undoubtedly belongs to the people of the United States of America. The geographical character of their vast country, not less than the sanguine and enterprising spirit of the nation, contributed to this. A coast of four thousand miles in extent, stretching from the Gulf of St. Lawrence to the embouchures of the Mississippi, indented and [Pg488] serrated in every part with natural harbours and sheltered bays, and fringed with islands forming sounds—capes, and promontories enclosing arms of the sea, in which the waters are free from the roll of the ocean, and take the placid character of lakes,—rivers of imposing magnitude, navigable for vessels of the largest class, for many hundreds and in some instances for many thousands of miles, affording access to the innermost population of an empire, whose area vastly exceeds the whole European continent,—chains of lakes composed of the most extensive bodies of fresh water in the known world,—and this extensive continent peopled by races carrying with them the habits and feelings together with much of the skill and knowledge of the most civilized parts of the globe, endowed also with that inextinguishable spirit of enterprise which ever belongs to an emigrant people,—form a combination of circumstances more than sufficient to account for the fact of this nation snatching from England, the parent of the steam engine, the honour of first bringing into practical operation one of the most important—if indeed it be not altogether the most important—of the many applications of that machine to the uses of life.

The circumstances which rendered these extensive tracts of inland and coast navigation eminently suited to the application of steam power, formed so many obstructions and difficulties to the application of other more ordinary means of locomotion on water. The sheltered bays and sounds which offered a smooth and undisturbed surface to the action of the infant steamer argued the absence of that element which gave effect to the sails and rigging of the wind-propelled ship, and the rapid currents of the gigantic streams formed by the drainage of this great continent, though facilitating access to the coast, rendered the oar powerless in the ascent.

(229.) The first great discovery of Watt had scarcely been realized in practice by the construction of the single-acting steam-engine, when the speculative and enterprising Americans conceived the project of applying it as a moving power in their inland navigation. So early as the year 1783 [Pg489] Fitch and Rumsey made attempts to apply the single-acting engine to the propulsion of vessels, and their failure is said to have arisen more from the inherent defects of that machine in reference to this application of it, than from any want of ingenuity or mechanical skill on their parts. In 1791, John Stevens of Hoboken commenced his experiments on steam navigation, which were continued for sixteen years; during a part of this period he was assisted by Livingstone (who was subsequently instrumental in advancing the views of Fulton), and by Roosevelt. These projectors had, at that time also, the assistance and advice of Brunel, since so celebrated for the invention of the block machinery, and the construction of the Thames Tunnel. Their proceedings were interrupted by the appointment of Livingstone as American Minister at Paris, under the Consular Government.

At Paris, Livingstone met Fulton, who had been previously engaged in similar speculations, and being struck with his mechanical skill, and the soundness of his views, joined him in causing a series of experiments to be made, which were accordingly carried on at Plombières, and subsequently on a still more extensive scale on the Seine, near Paris. Having by this course of experiments obtained proofs of the efficiency of Fulton's projects, sufficient to satisfy the mind of Livingstone, he agreed to obtain for Fulton the funds necessary to construct a steam boat on a large scale, to be worked upon the Hudson. It was decided, in order to give the project the best chance of success, to obtain the machinery from Bolton and Watt. In 1803, Fulton accordingly made drawings of the engines intended for this first steamer, which were sent to Soho, with an order for their construction. Fulton, meanwhile, repaired to America, to superintend the construction of the boat. The delays incidental to these proceedings retarded the completion of the boat and machinery until the year 1807, when all was completed, and the first successful experiment made at New York. The vessel was placed, for regular work, to ply between New York and Albany, in the beginning of 1808; and, from that time to the present, this river has been the theatre of the most [Pg490] remarkable series of experiments on locomotion on water which has ever been presented in the history of navigation.

(230.) The form and arrangement of this first marine engine was, in many respects, similar to that which is still generally used for marine purposes. The cold water cistern was abandoned, and an increased condensing power obtained by enlarging the condenser. It was usual to make the condenser half the diameter of the cylinder, and half its length, and therefore one eighth of its capacity. The condenser, however, was now made of the same diameter as the cylinder, being still half its length; its capacity therefore, instead of being only an eighth, was half of the cylinder; the condensing jet was admitted by a pipe passing through the bottom of the vessel. As in the present marine engines, two working beams were provided, one at either side of the cylinder; but in order to provide against the difficulties which might arise in the adaptation of machinery made at Birmingham to a vessel made at New York, beams were constructed in the form of an inverted ┻, the working arms being twofold, one horizontal and the other vertical, so that the connecting rod might be carried from the crank, either downwards, to the end of the horizontal arm, or horizontally, to the end of the vertical arm. In fact there was a choice, to use either a straight beam, or a bell-crank. The latter was that which was adopted in this instance. The paddle-shaft, driven by the crank, passed across the vessel, and had the paddle-wheels keyed upon it as at present; and in order to equalise the effect of the engine spur wheels were also placed on the paddle-shaft, by which pinions were driven, placed upon an axle, which carried a fly-wheel.

The speed attained by this steam boat, when it first began to ply upon the river, did not exceed four miles an hour, but by a series of improvements its rate of motion was soon increased to six miles an hour. In the steam boats subsequently constructed by Fulton a greater speed was attained; but in the latest vessels built by him he did not exceed a speed of nine miles an hour, which he considered to be the greatest that could be advantageously obtained.

While Fulton was making his plans, and engaged in the [Pg491] construction of his first boat, Mr. Stevens of Hoboken, already mentioned, was engaged in a like project, and completed a vessel, to be propelled by a steam engine, within a few weeks after the first successful voyage of Fulton. Stevens was likewise completely successful; but the exclusive privilege of navigating the Hudson by steam having been granted to Fulton by an act of Congress, Stevens was compelled to select another theatre for his operations, and he accordingly sent his steam boat by sea to Philadelphia, to navigate the Delaware, thus securing for himself the honour of having made the first sea voyage by steam.

Fulton did not long retain the monopoly of the steam navigation of the Hudson. Fortunately for the progress of steam navigation, the act conferring upon him that privilege was declared unconstitutional; and the navigation of that noble river was thrown open to the spirit and enterprise of American genius. The number of passengers conveyed upon it became enormous beyond all precedent, and inducements of the strongest kind were accordingly held out to the improvement of its navigation. The distance between New York and Albany, ascertained by a late survey to be one hundred and twenty-five geographical miles by water, had been performed by Fulton's boats occasionally in fifteen or sixteen hours, being at the rate of about eight miles an hour, including stoppages. It became a great object to increase the speed of this trip, so that it might at all times of the year be performed between sunrise and sunset. Robert L. Stevens, the son of the person of that name already mentioned, immediately after the abolition of Fulton's monopoly, placed on the river a vessel which had been built for the Delaware, which easily performed the passage in twelve hours, being at the rate of nearly ten and a half geographical miles an hour. By this increase of speed the improved boats so entirely monopolised the day work upon the river, that the former steamers were either converted into steam tugs to draw barges laden with goods, or used for night trips between New York and Albany. In the night trips the saving of one or two hours was immaterial, it being sufficient that the vessel which left the one port at night should reach the other in the morning. [Pg492]

The river Hudson rises near Lake Champlain, the easternmost of the great chain of lakes or inland seas which extend from east to west across the northern boundary of the United States. The river follows nearly a straight course southwards for two hundred and fifty miles, and empties itself into the sea at New York. The influence of the tide is felt as far as Albany, above which the stream begins to contract. Although this river in magnitude and extent is by no means equal to several others which intersect the States, it is nevertheless rendered an object of great interest by reason of the importance and extent of its trade. The produce of the state of New York and that of the banks of the great Lakes Ontario and Erie are transported by it to the capital; and one of the most extensive and populous districts of the United States is supplied with the necessary imports by its waters. A large fleet of vessels is constantly engaged in its navigation; nor is the tardy but picturesque sailing vessel as yet excluded by the more rapid steamers. The current of the Hudson is said to average nearly three miles an hour; but as the ebb and flow of the tide are felt as far as Albany, the passage of the steamers between that place and New York may be regarded as equally affected by currents in both directions, or nearly so. The passage therefore, whether in ascending or descending the river, is made nearly in the same time.

(231.) The prevalence of smooth water navigation, whether on the surfaces of rivers or in sheltered bays and sounds, has invested the problem of steam navigation in America with conditions so entirely distinct and different from those under which the same problem presents itself to the European engineer, that any comparison of the performance of vessels, whether with regard to speed or the absorption of power in the two cases, must be utterly fallacious. In Europe a steamer is almost invariably a vessel designed to encounter the agitated surface of an open sea, and is accordingly constructed upon principles of suitable strength and stability. It is likewise supplied with rigging and with sails, to be used in aid of the mechanical power, and manned and commanded by experienced seamen; in fact, it is a combination of a nautical and mechanical structure. In America, on the other hand, [Pg493] with the exception of the vessels which navigate the great northern lakes, the steamers are structures exclusively mechanical, being designed for smooth water. They require no other strength or stability than that which is sufficient to enable them to float and to bear a progressive motion through the water. Their mould is conceived with an exclusive view to speed; they are therefore slender and weak in their build, of great length in proportion to their width, and having a very small draught of water. In fact, they approach in their form to that of a Thames wherry on a very large scale.

The position and form of the machinery is likewise affected by these conditions. Without the necessity of being protected from a rough sea, it is placed on the deck in an elevated position. The cylinders of large diameter and short stroke invariably used in Europe are unknown in America, and the proportions are reversed, a small diameter and stroke of great length being invariably adopted. It is rarely that two engines are used. A single engine, placed in the centre of the deck, with a cylinder from forty to sixty inches' diameter, and from eight to ten foot stroke, drives paddle-wheels from twenty-one to twenty-five feet in diameter, producing from twenty-five to thirty revolutions per minute. The great magnitude of the paddle-wheels and the velocity imparted to them enable them to perform the office of fly-wheels, and to carry the engine round its centres, not however without a perceptible inequality of motion, which gives to the American steamer an effect like that of a row boat advancing by starts with each stroke of the piston. The length of stroke adopted in these engines enables them to apply with great effect the expansive principle, which is almost universally used, the steam being generally cut off at half stroke.

The steamers which navigate the Hudson are vessels of considerable magnitude, splendidly fitted up for the accommodation of passengers; they vary from one hundred and eighty to two hundred and forty feet in length, and from twenty to thirty feet in width of beam. In the following table is given the particulars of nine steamers plying on this river, taken from [Pg494] the work of Mr. Stevenson, and from the paper of Mr. Renwick, inserted in the last edition of Tredgold:—

————————————————————————————————————————————————————————————— | Length | Breadth | Draft | Drain | Length Names. | of | of | of | of | of | Deck. | Beam. | Water. | Wheel. | Paddles. ————————————————————————————————————————————————————————————— | Ft. | Ft. | Ft. | Ft. | Ft. Dewit Clinton | 230 | 28 | 5·5 | 21 | 13·7 Champlain | 180 | 27 | 5·5 | 22 | 15 Erie | 180 | 27 | 5·5 | 22 | 15 North America | 200 | 30 | 5 | 21 | 13 Independence | 148 | 26 | —— | —— | —— Albany | 212 | 26 | —— | 24·5 | 14 Swallow | 233 | 22·5 | 3·75 | 24 | 11 Rochester | 200 | 25 | 3·75 | 23·5 | 10 Utica | 200 | 21 | 3·5 | 22 | 9·5 —————————————————————————————————————————————————————————————

————————————————————————————————————————————————————————————————————— | Depth | Number | Drain | Length| Number | Part of Names. | of | of | of | of | of | Stroke | Paddles| Engines| Cylinder| Stroke| Revs | at which | | | | | | it is | | | | | | cut off. ————————————————————————————————————————————————————————————————————— | In. | | In. | Ft. | | Dewit Clinton | 36 | 1 | 65 | 10 | 29 | 3/4 Champlain | 34 | 2 | 44 | 10 | 27·5 | 1/2 Erie | 34 | 2 | 44 | 10 | 27·5 | 1/2 North America | 30 | 2 | 44·5 | 8 | 24 | 1/2 Independence | —— | 1 | 44 | 10 | | Albany | 30 | 1 | 65 | —— | 19 | Swallow | 30 | 1 | 46 | —— | 27 | Rochester | 24 | 1 | 43 | 10 | 28 | Utica | 24 | 1 | 39 | 10 | | —————————————————————————————————————————————————————————————————————

None of these vessels have either masts or rigging, and consequently never derive any propelling power except from the engines: they are neither manned nor commanded by persons having any knowledge of navigation: the works that are visible above their decks are the beam and framing of the engine, and the chimneys.

The engines used for steamers on the Hudson, and other great rivers and bays on the eastern coast of America, are most commonly condensing engines, but they nevertheless work with steam of very high pressure, being seldom less than twenty-five pounds per square inch, and sometimes as much as fifty. By reference to the preceding table it will be seen, that the velocity of the piston greatly exceeds the limit generally observed in Europe. It is customary in European marine engines to limit the speed of the piston to about two hundred and twenty feet per minute. Even the piston of a locomotive engine does not much exceed the rate of three hundred feet per minute. In the American steamers, however, the pistons commonly move at the rate of from five to six hundred feet per minute, while the circumference of the paddle-wheels are driven at the rate of from twenty to twenty-two miles an hour. [Pg495]

[Illustration: _Fig._ 135.]

The hulls of these boats are formed with a perfectly flat bottom and perpendicular sides, rounded at the angles, as represented in _fig._ 135. At the bow, or cutwater, they are made very sharp, and the deck projects to a great distance over the sides. The weight of the machinery is distributed over an extensive surface of the bottom of this feeble structure, by means of a frame-work of substantial carpentry to which it is attached.

At the height of from four to six feet above the water-line is placed the deck, which is a platform, having the shape of a very elongated ellipse. The extremities of its longer axis are supported by the sternpost and the cutwater, and its sides expand in gentle curves on either hand to a considerable distance beyond the limits of the hull; those parts of the deck thus overhanging the water are called the wheel guards.

Beneath the first deck is the saloon, or dining-room, which also, as is usual in European steamers, forms the gentlemen's sleeping-room. It usually extends from end to end of the vessel. The middle of the first deck is occupied by the engine, boilers, furnaces, and chimneys, of which latter there are generally two. Between the chimneys and the stern, above the first deck, is constructed the ladies' cabin, which is covered by the second deck, called the promenade deck. The great length of these boats and the elevation of the cabins render it impossible for a steersman at the stern to see ahead, and they are, consequently, steered from the bow; the wheel placed there communicating with the helm at the stern, by chains or rods carried along the sides of the boat. Until a recent period, the wheel was connected with the stern by ropes, but some fatal accidents, produced by fire, [Pg496] in which these ropes were burnt, and the steersman lost all power to guide the vessel, caused metal rods or chains to be substituted.

(232.) The paddle-wheels universally used in American steam-boats are formed, as if by the combination of two or more common paddle-wheels, placed one outside the other, on the same axle, but so that the paddle boards of each may have an intermediate position between those of the adjacent one, as represented in _fig._ 136.

[Illustration: _Fig._ 136.]

The spokes, which are bolted to cast-iron flanges, are of wood. These flanges, to which they are so bolted, are keyed upon the paddle shaft. The outer extremities of the spokes are attached to circular bands or hoops of iron, surrounding the wheel; and the paddle boards, which are formed of hard wood, are bolted to the spokes. The wheels thus constructed, sometimes consist of three, and not unfrequently four, independent circles of paddle boards, placed one beside the other, and so adjusted in their position, that the boards of no two divisions shall correspond.

The great magnitude of the paddle-wheels, and the circumstance of the navigation being carried on, for the most part, in smooth water, have rendered unnecessary, in America, the adoption of any of those expedients for neutralising the effects of the oblique

## action of the paddles, which have been tried, but hitherto with so

little success, in Europe.

(233.) Sea-going steamers are not numerous in America, the chief of them being those which ply between New York and Providence, and between New York and Charleston. These vessels, however, do not resemble the sea-going steamers of Europe as closely as might be expected; and to those who are accustomed to the latter, the sea-going [Pg497] steamers of America can hardly be regarded as safe means of transport.

In the following Table is given the dimensions of five of these vessels, all plying between New York and Providence:—

—————————————————————————————————————————————————————————————— | Length | Breadth | Draft | Diameter | Length Names. | of | of | | of | of | Deck. | Beam. | | Wheel. | Paddles. —————————————————————————————————————————————————————————————— | Ft. | Ft. | Ft. | Ft. | Ft. Providence | 180 | 27 | 9 | —— | —— Lexington | 207 | 21 | —— | 23 | 9 Narragansett | 210 | 26 | 5 | 25 | 11 Massachusetts | 200 | 29·5 | 8·5 | 22 | 10 Rhode Island | 210 | 26 | 6·5 | 24 | 11 —————————————————————————————————————————————————————————————— ————————————————————————————————————————————————————————————————————— | Depth | Number | Diameter| Length| Number | Part of Names. | of | of | of | of | of | Stroke | Paddles| Engines| Cylinder| Stroke| Revs | at which | | | | | | it is | | | | | | cut off. ————————————————————————————————————————————————————————————————————— | In. | | In. | Ft. | | Providence | —— | 1 | 10 | 65 | | Lexington | 30 | 1 | 11 | 48 | 24 | Narragansett | 30 | 1 | 60 | 12 | 2 | 1/2 Massachusetts | 28 | 2 | 44 | 8 | 26 | Rhode Island | 30 | 1 | 11 | 60 | 21 | —————————————————————————————————————————————————————————————————————

The Narragansett, the finest of these vessels, is built of oak, strengthened by diagonal straps or ties of iron, by which her timbers are connected; she is driven by a condensing engine, and has two boilers, exposing about three thousand square feet of surface to the fire. The steam is maintained at a pressure of from twenty to twenty-five lbs. per square inch: the cylinder is horizontal.

The cabins of these sea-boats are of great magnitude, and afford excellent accommodation for passengers, containing generally four hundred berths. In the Massachusetts the chief cabin is one hundred and sixty feet long, twenty-two feet wide, and twelve feet in height, its vast extent being uninterrupted by pillars or any other obstruction. "I have dined," says Mr. Stevenson, "with one hundred and seventy-five persons in this cabin, and, notwithstanding this numerous assembly, the tables, which were arranged in two parallel rows, extending from one end of the cabin to the other, were far from being fully occupied, the attendance was good, and every thing was conducted with perfect regularity and order. There are one hundred and twelve fixed berths ranged round this cabin, and one hundred temporary berths can be erected in the middle of the floor: besides these there are sixty fixed berths in the ladies' cabin, and several temporary sleeping [Pg498] places can be erected in it also. The cabin of the Massachusetts is by no means the largest in the United States. Some steamers have cabins upwards of one hundred and seventy-five feet in length. Those large saloons are lighted by Argand lamps, suspended from the ceiling, and their appearance, when brilliantly lighted up and filled with company, is very remarkable. The passengers generally arrange themselves in parties at the numerous small tables into which the large tables are converted after dinner, and engage in different amusements. The scene resembles much more the coffee-room of some great hotel than the cabin of a floating vessel."

(234.) Nothing has excited more surprise among engineers and others interested in steam navigation in Europe, than the statements which have been so generally and so confidently made of the speed attained by American steamers. This astonishment is due to several causes, the chief of which is the omission of all notice of the great difference between the structure and operation of the American steamers and the nature of the navigation in which they are engaged, compared with the structure and operation of, and the navigation in which European steamers are employed: as well might the performance of a Thames wherry, or one of the fly-boats on the northern canals, be compared with that of the Great Western, or the British Queen. The statements alluded to all have reference to steamers navigating the Hudson between New York and Albany, the form and structure of which we have already described; and doubtless the greatest speed ever attained on the surface of water has been exhibited in the passages of these vessels.

Mr. Stevenson states, that exclusive of the time lost in stoppages, the voyage between New York and Albany is usually made in ten hours. Dr. Renwick, however, who has probably more extensive opportunities of observation, states, that the average time, exclusive of stoppages, is ten hours and a half. The distance being 125·18 geographical miles, the average rate would therefore be 11-9/10 miles per hour. If it be observed that the average rate of some of the best sea-going steamers in Europe obtained from experiments [Pg499] and observations made by myself, more than three years ago, showed a rate of steaming little less than ten geographical miles per hour, and that since that time considerable improvements in steam navigation have been made, and further, that these performances were made under exposure to all the disadvantages of an open sea, the difference between them and the performance of the American river steamers will cease to create astonishment.

Dr. Renwick states that he made, in a boat called the "New Philadelphia," one of the most remarkable passages ever performed. He left New York at five in the afternoon, with the first of the flood, and landed at Catskill, distant 95·8 geographical miles from New York, at a quarter before twelve. Passengers were landed and taken in at seven intermediate points: the rate, including stoppages, was therefore 14·2 miles per hour; and if half an hour be allowed for stoppages, the actual average rate of motion would be fifteen miles and three quarters an hour. As the current, which in this case was with the course of the vessel, did not exceed three miles and a half an hour, the absolute velocity through the water would have been somewhat under twelve miles an hour. This speed is nearly the same as the speed obtained from taking the average time of the voyages between New York and Albany at ten hours and a half; it would therefore appear that the great speed attained in this trip must have been chiefly, if not altogether, owing to the effect of the current.

(235.) The steamers which navigate the great northern lakes differ so little in their construction and appearance from the European steam-boats, that it will not be necessary here to devote any considerable space to an account of them. These vessels were introduced on the lakes at about the same time that steamers were first introduced on the Clyde. These steamers are strongly built vessels, supplied with sails and rigging, and propelled by powerful engines. The largest in 1837, when Mr. Stevenson visited the States, was the _James Madison_. This vessel was one hundred and eighty-one feet in length on the deck, thirty feet in breadth of beam, and twelve feet six inches in depth of hold: her draught of water was ten feet, and her measured capacity seven hundred [Pg500] tons. She plyed between Buffalo on Lake Erie and Chicago on Lake Michigan, a distance of nine hundred and fifty miles.

The severe storms and formidable sea encountered on the lakes render necessary for the navigation, vessels in all respects as strong and powerful as those which navigate the open ocean.

(236.) By far the most remarkable and important of all the American rivers is the Mississippi and its tributaries. That part of the American continent which extends from the southern shores of the great northern lakes to the northern shores of the Gulf of Mexico, is watered by these great streams. The main stream of the Mississippi has its fountains in the tract of country lying north of the Illinois and east of Lake Michigan, in latitude forty-three degrees. At about latitude thirty-nine degrees, a little north of St. Louis, it receives the waters of the Missouri, and further south, at the latitude of thirty-seven degrees, the Ohio flows into it, after traversing five degrees of longitude and four of latitude, and winding its way from the Alleghany range through several of the states, and forming a navigable communication with numerous important towns of the Union, among which may be mentioned Pittsburg, Cincinnati, Frankfort, Lexington, and Louisville. The main stream of the Mississippi, after receiving the waters of the Arkansas, and numerous other minor tributaries, flows into the Gulf of Mexico by four mouths. The main stream of the Mississippi, independently of its tributaries, forms an unbroken course of inland navigation for a distance of nearly two thousand three hundred miles. Its width, through a distance of one thousand one hundred miles from its mouth, is not less than half a mile, and its average depth a hundred feet. The Ohio, its chief eastern tributary, flowing into it at a distance of about a thousand miles from its mouth, traverses also about the same extent of country, and is navigable throughout the whole of that extent. This river also has several navigable tributaries of considerable extent, among which may be mentioned the Muskingum, navigable for one hundred and twenty miles; the Miami, navigable for seventy-five miles; the Scioto, navigable for one hundred and twenty [Pg501] miles; the Tennessee, navigable for two hundred and fifty miles; the Cumberland, navigable for four hundred and forty miles; the Kentucky, navigable for one hundred and thirty miles; and the Green River, navigable for one hundred and fifty miles. The total length of the Ohio and its tributaries is estimated at above seven thousand miles.

(237.) Steam-boats were introduced on the Mississippi about the year 1812, the period of their first introduction in Europe; and their increase has been rapid beyond all precedent. In the year 1831 there were one hundred and ninety-eight steamers plying on its waters; and the number in 1837 amounted to nearly four hundred. These vessels are built chiefly on the banks of the Ohio, at the towns of Pittsburg and Cincinnati, at distances of about two thousand miles from the mouth of the river they are intended to navigate.

(238.) These steamers, which are decidedly inferior to those which navigate the eastern waters, are generally of a heavy build, fitted to carry goods as well as passengers, and vary from one hundred to seven hundred tons burthen. Their draught of water is also greater than that of the eastern river steamers—varying from six to eight feet. The hull, at about five feet from the water line, is covered with a deck, under which is the hold, in which the heavy part of the cargo is stowed. About the middle of this deck the engines are placed, the boilers and furnaces occupying a space nearer to the bow, near which two chimneys are placed. The fire-doors of the furnaces are presented towards the bow, and exposed so as to increase the draught. That part of the first deck which extends from the machinery to the stern is the place allotted to the crew and the deck passengers, and is described as being filthy and inconvenient in the extreme. A second deck is constructed, which extends from the chimneys near the bow to the stern of the vessel. On this is formed the great cabin or saloon, which extends from the chimneys to within about thirty feet of the stern, where it is divided by a partition from the ladies' cabin, which occupies the remaining space. These principal cabins are surrounded by a gallery about three feet in width, from which, at convenient [Pg502] places, an ascent is supplied by stairs to the highest deck, called the hurricane or promenade deck.

(239.) The engines by which these boats are propelled are totally different from the machinery already described as used in the eastern steamers. They are invariably non-condensing engines, worked by steam of extremely high pressure; the boilers are therefore tubular, and the cylinders small in diameter, but generally having a long stroke.

The pressure of steam used in these machines is such as is never used in European engines, even when worked on railways. A pressure of one hundred pounds per inch is here considered extremely moderate. The captain of one of these boats, plying between Pittsburg and St. Louis, told Mr. Stevenson that "under ordinary circumstances his safety valves were loaded with a pressure equal to one hundred and thirty-eight pounds per square inch, but that the steam was occasionally raised as high as one hundred and fifty pounds to enable the vessel to pass parts of the river in which there is a strong current;" and he added, by way of consolation, that "this pressure was never exceeded except on _extraordinary occasions_!"

The dimensions and power of the Mississippi steamers may be collected from those of the St. Louis, a boat which was plying on that river in 1837. That vessel measured two hundred and fifty feet on deck, and had twenty-eight feet breadth of beam. Her draught of water was eight feet, and her measured capacity one thousand tons. She was propelled by two engines with thirty-inch cylinders, and ten feet stroke; the safety valve being loaded at one hundred pounds per square inch.

The paddle wheels of these vessels are attached to the paddle shaft, in such a manner as to be thrown into and out of gear, at discretion, by the engineer, so that the paddle shaft may revolve without driving the wheels: by this expedient the power of the engine is used to feed the boilers while the vessel stops at the several stations. The vessel is therefore stopped, not, as is usually the case, by stopping the engines, but by throwing the wheels out of connection with the paddle shaft. The engines continue to work, but their [Pg503] power is expended in forcing water into the boiler. By this expedient the activity of the engines may, within practical limits, be varied with the resistance the vessel has to encounter. In working against a strong current, the feed may be cut off from the boilers, and the production of steam, and consequently the power of the engines, thereby stimulated, while this suspension of the feed may be compensated at the next station.

The stoppages to take in goods and passengers, and for relays of fuel, are frequent. "The liberty which they take with their vessels on these occasions," says Mr. Stevenson, "is somewhat amusing: I had a good example of this on board a large vessel, called the Ontario. She was steered close in shore amongst stones and stumps of trees, where she lay for some hours to take in goods: the additional weight increased her draught of water, and caused her to heel a good deal; and when her engines were put in motion, she actually _crawled_ into the deep water on her paddle wheels: the steam had been got up to an enormous pressure to enable her to get off, and the volume of steam discharged from the escapement pipe at every half stroke of the piston made a sharp sound almost like the discharge of fire-arms, while every timber in the vessel seemed to tremble, and the whole structure actually groaned under the shocks."

Besides the steamers used for the navigation of the Mississippi, innumerable steam tugs are constantly employed in towing vessels between the port of New Orleans and the open sea of the Gulf of Mexico. Before the invention of steam navigation, this southern capital of the United States laboured under the disadvantage of possessing almost the only bad and inconvenient harbour in the vast range of coast by which the country is bounded. New Orleans lies at a distance of about one hundred miles from the Gulf of Mexico. The force of the stream, the frequency of shoals, and the winding course of the channel rendered it scarcely possible for a sailing vessel to pass between the port and the sea with the same wind. The anchorage was every where bad, and great difficulty and risk attended the mooring of large vessels to the banks. The steam engine has, however, overcome all [Pg504] these difficulties, and rendered the most objectionable harbour of the Union a safe and good seaport, perfectly easy of approach and of egress at all times; a small steam tug will take in tow several large ships, and carry them with safety and expedition to the offing, where it will dismiss them on their voyage, and take back vessels which may have arrived.

[Illustration: GREAT WESTERN OFF NEW YORK.]

[Pg505]

APPENDIX.

_On the Relation between the Temperature, Pressure, and Density_ _of Common Steam._

There is a fixed relation between the temperature and pressure of common steam, which has not yet been ascertained by theory. Various empirical formulæ have been proposed to express it, derived from tables of temperatures and corresponding pressures which have been founded on experiments and completed by interpolation.

The following formula, proposed by M. Biot, represents with great accuracy the relation between the temperature and pressure of common steam, throughout all that part of the thermometric scale to which experiments have been extended.

Let

a = 5·96131330259 log. a_{1} = 0·82340688193 − 1 log. b_{1} = −·01309734295 log. a_{2} = 0·74110951837 log. b_{2} = −·00212510583

The relation between the temperature t with reference to the centesimal thermometer, and the pressure p in millimètres of mercury at the temperature of melting ice, will then be expressed by the following formula:—

log. p = a − a_{1}b_{1}^{20 + t} − a_{2}b_{2}^{20 + t}. (1.)

Formulæ have, however, been proposed, which, though not applicable to the whole scale of temperatures, are more manageable in their practical application than the preceding.

For pressures less than an atmosphere, Southern proposed the following formula, where the pressure is intended to be expressed [Pg506] in pounds per square inch, and the temperature in reference to Fahrenheit's thermometer,—

p = 0·04948 + ((51·3 + t) / 155·7256)^{5·13} | |. (2.) t = 155·7256 ((p − 0·04948) − 51·3)^{1/(5·13)} |

The following formula was proposed by Tredgold, where p expresses the pressure in inches of mercury:—

p = ((100 + t) / 177)^{6}.

This was afterwards modified by Mellet, and represents with sufficient accuracy experiments from 1 to 4 atmospheres. Let p represent pounds per square inch, and t the temperature by Fahrenheit's thermometer,—

p = ((103 + t) / 201·18)^{6} | |. (3.) t = 201·18 p^{1/6} − 103 |

M. de Pambour has proposed the following formula, also applicable through the same limits of the scale:—

p = ((98·806 + t) / 198·562)^{6} | |. (4.) t = 198·562 p^{1/6} − 98·806 |

MM. Dulong and Arago have proposed the following formula for all pressures between 4 and 50 atmospheres:—

p = (0·26793 + 0·0067585 t)^{5} | |. (5.) t = 147·961 p^{1/5} − 39·644 |

It was about the year 1801, that Dalton, at Manchester, and Gay-Lussac, at Paris, instituted a series of experiments on gaseous bodies, which conducted them to the discovery of the law mentioned in art. (96.), p. 171. These philosophers found that all gases whatever, and all vapours raised from liquids by heat, as well as all mixtures of gases and vapours, are subject to the _same quantity of expansion_ between the temperatures of melting ice and boiling water; and by experiments subsequently made by Dulong and Petit, this uniformity of expansion has been proved to extend to all temperatures which can come under practical inquiries.

Dalton found that 1000 cubic inches of air at the temperature of melting ice dilated to 1325 cubic inches if raised to the temperature of boiling water. According to Gay-Lussac, the increased volume was 1375 cubic inches. The latter determination has been subsequently found to be the more correct one.[40]

[Pg507] It appears, therefore, that for an increase of temperature from 32° to 212°, amounting to 180°, the increase of volume is 375 parts in 1000; and since the expansion is uniform, the increase of volume for 1° will be found by dividing this by 180, which will give an increase of 208-1/3 parts in 100,000 for each degree of the common thermometer.

To reduce the expression of this important and general law to mathematical language, let v be the volume of an elastic fluid at the temperature of melting ice, and let nv be the increase which that volume would receive by being raised one degree of temperature under the same pressure. Let V be its volume at the temperature T. Then we shall have

V = v + nv (T − 32) = v (1 + n (T − 32)).

If V′ be its volume at any other temperature T′, and under the same pressure, we shall have, in like manner,

V′ = v (1 + n (T′ − 32)).

Hence we obtain

V/V′ = (1 + n (T − 32)) / (1 + n (T′ − 32)); (6.)

which expresses the relation between the volumes of the same gas or vapour under the same pressure and at any two temperatures. The co-efficient n, as explained in the text, has the same value for the same gas or vapour throughout the whole thermometric scale. But it is still more remarkable that this constant has the same value for all gases and vapours. It is a number, therefore, which must have some essential relation to the gaseous or elastic state of fluid matter, independent of the peculiar qualities of any

## particular gas or vapour.

The value of n, according to the experiments of Gay-Lussac, is 0·002083, or 1/480.

To reduce the law of Mariotte, explained in (97.) p. 171., to mathematical language, let V, V′ be the volumes of the same gas or vapour under different pressures P, P′, but at the same temperature. We shall then have

VP = V′P′. (7.)

If it be required to determine the relation between the volumes of the same gas or vapour, under a change of both temperature and pressure, let V be the volume at the temperature T and under the pressure P, and let V′ be the volume at the temperature T′ and under the pressure P′. Let v be the volume at the temperature T and under the pressure P′.

By formula (7.) we have

VP = vP′;

[Pg508] and by formula (6.) we have

(V′/v) = (1 + n(T′ − 32)) / (1 + n(T − 32))

Eliminating v, we shall obtain

(V/V′) = (P′/P) · (1 + n(T − 32)) / (1 + n(T′ − 32));

or,

(VP/V′P′) = (1 + n(T − 32)) / (1 + n(T′ − 32)); (8.)

which is the general relation between the volumes, pressures, and temperatures of the same gas or vapour in two different states.

To apply this general formula to the case of the vapour of water, let T′ = 212°. It is known by experiment that the corresponding value of P′, expressed in pounds per square inch, is 14·706; and that V′, expressed in cubic inches, the water evaporated being taken as a cubic inch, is 1700. If, then, we take 0·002083 as the value of n, we shall have by (8.),

VP = 1700 × 14·706 × (1 + 0·002083 (T − 32)) / (1 + 0·002083 × 180)

= 18183(1 + 0·002083 (T − 32)). (9.)

If, by means of this formula (9.), and any of the formulæ (1.), (2.), (3.), (4.), (5.), T were eliminated, we should obtain a formula between V and P, which would enable us to compute the enlargement of volume which water undergoes in passing into steam under any proposed pressure. But such a formula would not be suitable for practical computations. By the formulæ (1.) to (5.), a table of pressures and corresponding temperatures may be computed; and these being known, the formula (9.) will be sufficient for the computation of the corresponding values of V, or the enlargement of volume which water undergoes in passing into steam.

In the following table, the temperatures corresponding to pressures from 1 to 240 lbs. per square inch are given by computation from the formulæ (2.) to (5.), and the volumes of steam produced by an unit of volume of water as computed from the formula (9.).

The mechanical effect is obtained by multiplying the pressure in pounds by the expansion of a cubic inch of water in passing into steam expressed in feet, and is therefore the number of pounds which would be raised one foot by the evaporation of a cubic inch of water under the given pressure. [Pg509]

—————————————————————————————————————————————————————————— | | Volume of | Mechanical Total pressure| | the Steam | Effect of in Pounds | Corresponding| compared to | a Cubic Inch per Square | Temperature. | the Volume | of Water Inch. | | of the | evaporated | | Water that | in Pounds | | has | raised One | | produced it.| Foot. ——————————————+——————————————+—————————————+————————————— 1 | 102·9 | 20868 | 1739 2 | 126·1 | 10874 | 1812 3 | 141·0 | 7437 | 1859 4 | 152·3 | 5685 | 1895 5 | 161·4 | 4617 | 1924 6 | 169·2 | 3897 | 1948 7 | 175·9 | 3376 | 1969 8 | 182·0 | 2983 | 1989 9 | 187·4 | 2674 | 2006 10 | 192·4 | 2426 | 2022 11 | 197·0 | 2221 | 2036 12 | 201·3 | 2050 | 2050 13 | 205·3 | 1904 | 2063 14 | 209·1 | 1778 | 2074 15 | 212·8 | 1669 | 2086 16 | 216·3 | 1573 | 2097 17 | 219·6 | 1488 | 2107 18 | 222·7 | 1411 | 2117 19 | 225·6 | 1343 | 2126 20 | 228·5 | 1281 | 2135 21 | 231·2 | 1225 | 2144 22 | 233·8 | 1174 | 2152 23 | 236·3 | 1127 | 2160 24 | 238·7 | 1084 | 2168 25 | 241·0 | 1044 | 2175 26 | 243·3 | 1007 | 2182 27 | 245·5 | 973 | 2189 28 | 247·6 | 941 | 2196 29 | 249·6 | 911 | 2202 30 | 251·6 | 883 | 2209 31 | 253·6 | 857 | 2215 32 | 255·5 | 833 | 2221 33 | 257·3 | 810 | 2226 34 | 259·1 | 788 | 2232 35 | 260·9 | 767 | 2238 36 | 262·6 | 748 | 2243 37 | 264·3 | 729 | 2248 38 | 265·9 | 712 | 2253 39 | 267·5 | 695 | 2259 40 | 269·1 | 679 | 2264 41 | 270·6 | 664 | 2268 42 | 272·1 | 649 | 2273 43 | 273·6 | 635 | 2278 44 | 275·0 | 622 | 2282 45 | 276·4 | 610 | 2287 46 | 277·8 | 598 | 2291 47 | 279·2 | 586 | 2296 48 | 280·5 | 575 | 2300 49 | 281·9 | 564 | 2304 50 | 283·2 | 554 | 2308 51 | 284·4 | 544 | 2312 52 | 285·7 | 534 | 2316 53 | 286·9 | 525 | 2320 54 | 288·1 | 516 | 2324 55 | 289·3 | 508 | 2327 56 | 290·5 | 500 | 2331 57 | 291·7 | 492 | 2335 58 | 292·9 | 484 | 2339 59 | 294·2 | 477 | 2343 60 | 295·6 | 470 | 2347 61 | 296·9 | 463 | 2351 62 | 298·1 | 456 | 2355 63 | 299·2 | 449 | 2359 64 | 300·3 | 443 | 2362 65 | 301·3 | 437 | 2365 66 | 302·4 | 431 | 2369 67 | 303·4 | 425 | 2372 68 | 304·4 | 419 | 2375 69 | 305·4 | 414 | 2378 70 | 306·4 | 408 | 2382 71 | 307·4 | 403 | 2385 72 | 308·4 | 398 | 2388 73 | 309·3 | 393 | 2391 74 | 310·3 | 388 | 2394 75 | 311·2 | 383 | 2397 76 | 312·2 | 379 | 2400 77 | 313·1 | 374 | 2403 78 | 314·0 | 370 | 2405 79 | 314·9 | 366 | 2408 80 | 315·8 | 362 | 2411 81 | 316·7 | 358 | 2414 82 | 317·6 | 354 | 2417 83 | 318·4 | 350 | 2419 84 | 319·3 | 346 | 2422 85 | 320·1 | 342 | 2425 86 | 321·0 | 339 | 2427 87 | 321·8 | 335 | 2430 88 | 322·6 | 332 | 2432 89 | 323·5 | 328 | 2435 90 | 324·3 | 325 | 2438 91 | 325·1 | 322 | 2440 92 | 325·9 | 319 | 2443 93 | 326·7 | 316 | 2445 94 | 327·5 | 313 | 2448 95 | 328·2 | 310 | 2450 96 | 329·0 | 307 | 2453 97 | 329·8 | 304 | 2455 98 | 330·5 | 301 | 2457 99 | 331·3 | 298 | 2460 100 | 332·0 | 295 | 2462 110 | 339·2 | 271 | 2486 120 | 345·8 | 251 | 2507 130 | 352·1 | 233 | 2527 140 | 357·9 | 218 | 2545 150 | 363·4 | 205 | 2561 160 | 368·7 | 193 | 2577 170 | 373·6 | 183 | 2593 180 | 378·4 | 174 | 2608 190 | 382·9 | 166 | 2622 200 | 387·3 | 158 | 2636 210 | 391·5 | 151 | 2650 220 | 395·5 | 145 | 2663 230 | 399·4 | 140 | 2675 240 | 403·1 | 134 | 2687 ——————————————+——————————————+—————————————+—————————————

[Pg511] In the absence of any direct method of determining the general relation between the pressure and volume of common steam, empirical formulæ expressing it have been proposed by different mathematicians.

The late Professor Navier proposed the following:—Let S express the volume of steam into which an unit of volume of water is converted under the pressure P, this pressure being expressed in kilogrammes per square mètre. Then the relation between S and P will be

S = a/(b + mP),

where a = 1000, b = 0·09, and m = 0·0000484.

This formula, however, does not agree with experiment at pressures less than an atmosphere. M. de Pambour, therefore, proposes the following changes in the values of its co-efficients:—Let P express the pressure in pounds per square foot; and let

a = 10000 b = 0·4227 m = 0·00258,

and the formula will be accurate for all pressures. For pressures above two atmospheres the following values give more accuracy to the calculation:—

a = 10000 b = 1·421 m = 0·0023.

In these investigations I shall adopt the following modified formula. The symbols S and P retaining their signification, we shall have

S = a/(b + P) (10.)

where

a = 3875969 b = 164.

These values of a and b will be sufficiently accurate for practical purposes for all pressures, and may be used in reference to low-pressure engines of every form, as well as for high-pressure engines which work expansively.

When the pressure is not less than 30 pounds per square inch, the following values of a and b will be more accurate:—

a = 4347826 b = 618.

_On the Expansive Action of Steam._

The investigation of the effect of the expansion of steam which has been given in the text, is intended to convey to those who are not conversant with the principles and language of analysis, some notion of the nature of that mechanical effect to which the advantages attending the expansive principle are due. We shall now, however, explain these effects more accurately. [Pg512]

The dynamical effect produced by any mechanical agent is expressed by the product of the resistance overcome and the space through which that resistance is moved.

Let P = the pressure of steam expressed in pounds per square foot. S = the number of cubic feet of steam of that pressure produced by the evaporation of a cubic foot of water. E = the mechanical effect produced by the evaporation of a cubic foot of water expressed in pounds raised one foot.

Then we shall have E = PS; and if W be a volume of water evaporated under the pressure P, the mechanical effect produced by it will be WPS.

By (10.) we have

SP = a − bS.

Hence, for the mechanical effect of a cubic foot of water evaporated under the pressure P we have

E = a − bS. (11.)

Let a cubic foot of water be evaporated under the pressure P′, and let it produce a volume of steam S′ of that pressure. Let this steam afterwards be allowed to expand to the increased volume S and the diminished pressure P; and let it be required to determine the mechanical effect produced during the expansion of the steam from the volume S′ to the volume S.

Let E′ = the mechanical effect produced by the evaporation of the water under the pressure P′ without expansion. E″ = the mechanical effect produced during the expansion of the steam. E = the mechanical effect which would be produced by the evaporation under the pressure P without expansion. _E_ = the total mechanical effect produced by the evaporation under the pressure P′ and subsequent expansion.

Thus we have

_E_ = E′ + E″.

Let s be any volume of the steam during the process of expansion, p the corresponding pressure, and e″ the mechanical effect produced by the expansion of the steam. We have then by (10.)

p = (a/s) − b;

∵ de″ = (ads/s) − bds.

Hence by integrating we obtain

e″ = a log. s − bs + C;

[Pg513] which, taken between the limits s = S′ and s = S, becomes

E″ = a log. S/S′ − b(S − S′). (12.)

But by (11.) we have

E′ = a − bS′, E = a − bS; ∵ E′ − E = b(S − S′); ∵ E″ = a log. S/S′ − E′ + E; ∵ _E_ = E″ + E′ = a log. S/S′ + E. (13.)

Or,

_E_ = a (1 + log. S/S′) − bS. (14.)

Hence it appears that the mechanical effect of a cubic foot of water evaporated under the pressure P may be increased by the quantity a log. S/S′, if it be first evaporated under the greater pressure P′, and subsequently expanded to the lesser pressure P.

The logarithms in these formulæ are hyperbolic.

To apply these principles to the actual case of a double acting steam engine,

Let L = the stroke of the piston in feet. A = the area of the piston in square feet. n = the number of strokes of the piston per minute. ∵ 2n AL = the number of cubic feet of space through which the piston moves per minute. Let cLA = the clearage, or the space between the steam valve and the piston at each end of the stroke. ∵ The volume of steam admitted through the steam valve at each stroke of the engine will be 2n AL(1 + c).

Let V = the mean speed of the piston in feet per minute, ∵ 2nL = V.

The volume of steam admitted to the cylinder per minute will therefore be VA (1 + c), the part of it employed in working the piston being VA.

Let W = the water in cubic feet admitted per minute in the form of steam through the steam valve. S = the number of cubic feet of steam produced by a cubic foot of water.

[Pg514] Hence we shall have

WS = VA (1 + c); ∵ S = (VA(1 + c))/W. (15.)

Since by (10.) we have

P = a/S − b; ∵ P = [Wa/(VA(1 + c))] − b. (16.)

By which the pressure of steam in the cylinder will be known, when the effective evaporation, the diameter of the cylinder, and speed of the piston, are given.

If it be required to express the mechanical effect produced per minute by the action of steam on the piston, it is only necessary to multiply the pressure on the surface of the piston by the space per minute through which the piston moves. This will give

VAP = W(a/(1 + c)) − VAb; (17.)

which expresses the whole mechanical effect per minute in pounds raised one foot.

If the steam be worked expansively, let it be cut off after the piston has moved through a part of the stroke expressed by e.

The volume of steam of the undiminished pressure P′ admitted per minute through the valve would then be

VA (e + c);

and the ratio of this volume to that of the water producing it being expressed by S′, we should have

S′ = (VA(e + c))/W.

The final volume into which this steam is subsequently expanded being VA(1 + c), its ratio to that of the water will be

S = (VA (1 + c))/W.

The pressure P′, till the steam is cut off, will be

P′ = [Wa / (VA(e + c))] − b. (18.)

The mechanical effect E′ produced per minute by the steam of full pressure will be

E′ = P′AVe = [Wae / (e + c)] − AVbe;

and the effect E″ per minute produced by the expansion of the steam will by (12.) be [Pg515]

E″ = Wa log.[(1 + c) / (e + c)] − bVA(1 − e).

Hence the total effect per minute will be

_E_ = Wa [(e/(e + c)) + log.([1 + c]/[e + c])] − bVA. (19.)

If the engine work without expansion, e = 1;

∵ _E′_ = ( Wa/(1 + c)) − bVA, (20.)

as before; and the effect per minute gained by expansion will therefore be

_E_ − _E′_ =

Wa [(e/(e + c)) − (1/(1 + c)) + log.([1 + c]/[e + c])]; (21.)

which therefore represents the quantity of power gained by the expansive action, with a given evaporating power.

In these formulæ the total effect of the steam is considered without reference to the nature of the resistances which it has to overcome.

These resistances may be enumerated as follows:—

1. The resistance produced by the load which the engine is required to move.

2. The resistance produced by the vapour which remains uncondensed if the engine be a condensing engine, or of the atmospheric pressure if the engine do not condense the steam.

3. The resistance of the engine and its machinery, consisting of the friction of the various moving parts, the resistances of the feed pump, the cold water pump, &c. A part of these resistances are of the same amount, whether the engine be loaded or not, and part are increased, in some proportion depending on the load.

When the engine is maintained in a state of uniform motion, the sum of all these resistances must always be equal to the whole effect produced by the steam on the piston. The power expended on the first alone is the _useful effect_.

Let R = the pressure per square foot of the piston surface, which balances the resistances produced by the load.

mR = the pressure per square foot, which balances that part of the friction of the engine which is proportional to the load.

r = the pressure per square foot, which balances the sum of all those resistances that are not proportional to the load.

The total resistance, therefore, being R + mR + r, which, when the mean motion of the piston is uniform, must be equal to the mean pressure on the piston. The total mechanical effect [Pg516] must therefore be equal to the total resistance multiplied by the space through which that resistance is driven. Hence we shall have

[R(1 + m) + r]VA = Wa[(e/(e + c)) + log.([1 + c]/[e + c])] − VAb;

∵ RVA(1 + m) = Wa[(e/(e + c)) + log.([1 + c]/[e + c])] − VA(b + r).

For brevity, let

e′ = a[(e/(e + c)) + log.([1 + c]/[e + c])];

∵ RVA(1 + m) = We′ − VA(b + r). (22.)

By solving this for VA, we obtain

VA = We′/(R(1 + m) + b + r);

∵ RVA = We′R/(R(1 + m) + b + r). (23.)

This quantity RVA, being the product of the resistance RA, of the load reduced to the surface of the piston, multiplied by the space through which the piston is moved, will be equal to the load itself multiplied by the space through which it is moved. This being, in fact, the useful effect of the engine, let it be expressed by U, and we shall have

U = We′R/(R(1 + m) + b + r). (24.)

Or by (22.),

U(1 + m) = We′ − VA(b + r). (25.)

The value of the useful effect obtained from these formulæ will be expressed in pounds, raised one foot per minute, W being the effective evaporation in cubic feet per minute, A the area of the piston in square feet, and V the space per minute through which it is moved, in feet.

Since a resistance amounting to 33,000 pounds moved through one foot per minute is called one-horse power, it is evident that the horse power H of the engine is nothing more than the useful effect per minute referred to a larger unit of weight or resistance; that is to 33,000 pounds instead of one pound. Hence we shall have

H = U/33000. (26.)

Since the useful effect expressed in (24.) and (25.) is that due to a number of cubic feet of water, expressed by W, we shall obtain the effect due to one cubic foot of water, by dividing U by W. If, therefore, U′ be the effect produced by the effective evaporation of a cubic foot of water, we shall have [Pg517]

U′ = U/W. (27.)

If the quantity of fuel consumed per minute be expressed by F, the effect produced by the unit of fuel, called the DUTY of the engine, will, for like reason, be

D = U/F. (28.)

If the fuel be expressed in hundredweights of coal, then D will express the number of pounds' weight raised one foot by a hundredweight of coal.

By solving (24.) and (25.) for W, we obtain

W = [U(R(1 + m) + b + r)]/Re′, (29.)

W = (1/e′)[U(1 + m) + VA(b + r)]. (30.)

By eliminating U, by (26.), we shall have

W = [33000 H(R(1 + m) + b + r)]/Re′, (31.)

W = (1/e′)[33000 H(1 + m) + VA(b + r)]. (32.)

The evaporation necessary per horse power per minute will be found by putting H = 1 in these formulæ.[41]

It will be observed that the quantities A and V, the area of the cylinder and the speed of the piston, enter all these formulæ as factors of the same product. Other things, therefore, being the same, the speed of the piston will be always inversely as the area of the cylinder. In fact, VA is the volume of steam per minute employed in working the piston, and if the piston be increased or diminished in magnitude, its speed must be inversely [Pg518] varied by the necessity of being still moved through the same number of cubic feet by the same volume of steam.

It has been already stated in the text, that no satisfactory experiments have yet been made, by which the numerical value of the quantity r can be exactly known. In engines of different magnitudes and powers, this resistance bears very different proportions to the whole power of the machine. In general, however, the larger and more powerful the engine, the less that proportion will be.

That part of this resistance which arises from the reaction of the uncondensed vapour on the piston is very variable, owing to the more or less perfect action of the condensing apparatus, the velocity of the piston, and the magnitude and form of the steam passages. M. de Pambour states, that, by experiments made with indicators, the mean amount of this resistance in the cylinder is 2-1/2 lbs. per square inch more than in the condenser, and that the pressure in the latter being usually 1-1/2 lb. per square inch, the mean amount of the pressure of the condensed vapour in the cylinder is about 4 lbs. per square inch. Engineers, however, generally consider this estimate to be above the truth in well-constructed engines, when in good working order.

In condensing low pressure engines of forty horse power and upwards, working with an average load, it is generally considered that the resistance produced by the friction of the machine and the force necessary to work the pumps may be taken at about 2 lbs. per square inch of piston surface.

Thus the whole resistance represented by r in the preceding formulæ, as applied to the larger class of low pressure engines, may be considered as being under 6 lbs. per square inch, or 864 lbs. per square foot, of the piston. It is necessary, however, to repeat, that this estimate must be regarded as a very rough approximation; and as representing the mean value of a quantity subject to great variation, not only in one engine compared with another, but even in the same engine compared with itself at different times and in different states.

In the same class of engines, the magnitude of the clearage is generally about a twentieth part of the capacity of the cylinder, so that c = 0·05.

That part of the resistance which is proportional to the load, and on which the value of m in the preceding formulæ depends, is still more variable, and depends so much on the form, magnitude, and the arrangement of its parts, that no general rule can be given for its value. It must, in fact, be determined in every particular case.

In the practical application of the preceding formulæ in condensing engines we shall have [Pg519]

a = 3875969 b = 164 c= 0·05;

e′ = 3875969([e/(e + 0·05)] + log.[1·05/(e + 0·05)]).

In engines which work without condensation, and therefore with high pressure steam, we shall have

a = 4347826 b = 618 c = 0·05

e′ = 4347826([e/(e + 0·05)] + log.[1·05/(e + 0·05)])

To facilitate computation, the values of e′ corresponding to all values of e, from e = ·10 to e = ·90, are given in the following table:—

——————————————————————————————————————————————————————————————— |Condensing|Non-condensing|| |Condensing|Non-condensing | Engines | Engines || | Engines | Engines e | e′. | e′. || e | e′. | e′. ————+——————————+——————————————++————+——————————+——————————————— ·10 | 10126265 | 11359029 ||·51 | 5966367 | 6692708 ·11 | 9956867 | 11169008 ||·52 | 5903837 | 6622565 ·12 | 9793136 | 10985344 ||·53 | 5842288 | 6553525 ·13 | 9634926 | 10807875 ||·54 | 5781693 | 6485552 ·14 | 9482029 | 10636364 ||·55 | 5722024 | 6418619 ·15 | 9334219 | 10470560 ||·56 | 5663251 | 6352693 ·16 | 9191251 | 10310186 ||·57 | 5605353 | 6287745 ·17 | 9052888 | 10154978 ||·58 | 5548297 | 6223742 ·18 | 8918896 | 10004675 ||·59 | 5492064 | 6160662 ·19 | 8789043 | 9859014 ||·60 | 5436628 | 6098478 ·20 | 8663120 | 9717760 ||·61 | 5381969 | 6037166 ·21 | 8540918 | 9580682 ||·62 | 5328065 | 5976699 ·22 | 8422242 | 9447559 ||·63 | 5274896 | 5917057 ·23 | 8306916 | 9318193 ||·64 | 5222444 | 5858219 ·24 | 8194770 | 9192396 ||·65 | 5170684 | 5800159 ·25 | 8085644 | 9069984 ||·66 | 5119605 | 5742860 ·26 | 7979392 | 8950796 ||·67 | 5069186 | 5686304 ·27 | 7875870 | 8834674 ||·68 | 5019410 | 5630469 ·28 | 7774952 | 8721468 ||·69 | 4970263 | 5575340 ·29 | 7676514 | 8611048 ||·70 | 4921727 | 5520894 ·30 | 7580447 | 8503284 ||·71 | 4873790 | 5467121 ·31 | 7486640 | 8398056 ||·72 | 4826434 | 5414000 ·32 | 7394990 | 8295250 ||·73 | 4779648 | 5361519 ·33 | 7305407 | 8194760 ||·74 | 4733417 | 5309659 ·34 | 7217807 | 8096496 ||·75 | 4687728 | 5258408 ·35 | 7132097 | 8000352 ||·76 | 4642569 | 5207751 ·36 | 7048206 | 7906249 ||·77 | 4597928 | 5157676 ·37 | 6966058 | 7814100 ||·78 | 4553794 | 5108170 ·38 | 6885585 | 7723832 ||·79 | 4510155 | 5059218 ·39 | 6806720 | 7635365 ||·80 | 4466999 | 5010808 ·40 | 6729408 | 7548642 ||·81 | 4424317 | 4962931 ·41 | 6653578 | 7463580 ||·82 | 4382096 | 4915569 ·42 | 6579187 | 7380132 ||·83 | 4340332 | 4868720 ·43 | 6506174 | 7298230 ||·84 | 4299010 | 4822368 ·44 | 6434491 | 7217822 ||·85 | 4258120 | 4776500 ·45 | 6364099 | 7138858 ||·86 | 4217658 | 4731113 ·46 | 6294944 | 7061285 ||·87 | 4177613 | 4686192 ·47 | 6226989 | 6985058 ||·88 | 4137974 | 4641728 ·48 | 6160190 | 6910126 ||·89 | 4098737 | 4597713 ·49 | 6094510 | 6836450 ||·90 | 4059893 | 4554140 ·50 | 6029916 | 6763992 || | | ————+——————————+——————————————++————+——————————+———————————————

[Pg520] In engines which work without expansion we have

e′ = a/(1 + c).

For condensing engines without expansion, we shall then have

e′ = 3875969/1·05 = 3691399; (33.)

and for non-condensing engines,

e′ = 4347826/1·05 = 4140787. (34.)

As the diameters of the cylinders of engines are generally expressed in inches, the corresponding areas of the pistons expressed in square feet are given in the following table, so that the values of A may be readily found:—

—————————————————————————————————————————————————————————————————————— Diam. | Area. | Diam. | Area. | Diam. | Area. | Diam. | Area. ———————+—————————+———————+—————————+———————+—————————+———————+———————— Inches.| Sq.feet.|Inches.| Sq.feet.|Inches.| Sq.feet.|Inches.| Sq.feet. 10 | 0·545 | 48 | 12·566 | 86 | 40·339 | 124 | 83·863 11 | 0·660 | 49 | 13·095 | 87 | 41·283 | 125 | 85·221 12 | 0·785 | 50 | 13·635 | 88 | 42·237 | 126 | 86·590 13 | 0·922 | 51 | 14·186 | 89 | 43·202 | 127 | 87·970 14 | 1·069 | 52 | 14·748 | 90 | 44·179 | 128 | 89·361 15 | 1·227 | 53 | 15·321 | 91 | 45·166 | 129 | 90·763 16 | 1·396 | 54 | 15·904 | 92 | 46·164 | 130 | 92·175 17 | 1·576 | 55 | 16·499 | 93 | 47·173 | 131 | 93·599 18 | 1·767 | 56 | 17·104 | 94 | 48·193 | 132 | 95·033 19 | 1·969 | 57 | 17·721 | 95 | 49·224 | 133 | 96·479 20 | 2·182 | 58 | 18·348 | 96 | 50·265 | 134 | 97·935 21 | 2·405 | 59 | 18·986 | 97 | 51·318 | 135 | 99·402 22 | 2·640 | 60 | 19·635 | 98 | 52·382 | 136 | 100·880 23 | 2·885 | 61 | 20·295 | 99 | 53·456 | 137 | 102·369 24 | 3·142 | 62 | 20·966 | 100 | 54·542 | 138 | 103·869 25 | 3·409 | 63 | 21·648 | 101 | 55·638 | 139 | 105·380 26 | 3·687 | 64 | 22·340 | 102 | 56·745 | 140 | 106·901 27 | 3·976 | 65 | 23·044 | 103 | 57·863 | 141 | 108·434 28 | 4·276 | 66 | 23·758 | 104 | 58·992 | 142 | 109·977 29 | 4·587 | 67 | 24·484 | 105 | 60·132 | 143 | 111·532 30 | 4·909 | 68 | 25·220 | 106 | 61·283 | 144 | 113·097 31 | 5·241 | 69 | 25·967 | 107 | 62·445 | 145 | 114·674 32 | 5·585 | 70 | 26·725 | 108 | 63·617 | 146 | 116·261 33 | 5·940 | 71 | 27·494 | 109 | 64·801 | 147 | 117·859 34 | 6·305 | 72 | 28·274 | 110 | 65·995 | 148 | 119·468 35 | 6·681 | 73 | 29·065 | 111 | 67·201 | 149 | 121·088 36 | 7·069 | 74 | 29·867 | 112 | 68·417 | 150 | 122·719 37 | 7·467 | 75 | 30·680 | 113 | 69·644 | 151 | 124·361 38 | 7·876 | 76 | 31·503 | 114 | 70·882 | 152 | 126·013 39 | 8·296 | 77 | 32·338 | 115 | 72·131 | 153 | 127·676 40 | 8·727 | 78 | 33·183 | 116 | 73·391 | 154 | 129·351 41 | 9·168 | 79 | 34·039 | 117 | 74·662 | 155 | 131·036 42 | 9·621 | 80 | 34·907 | 118 | 75·944 | 156 | 132·732 43 | 10·085 | 81 | 35·785 | 119 | 77·236 | 157 | 134·439 44 | 10·559 | 82 | 36·674 | 120 | 78·540 | 158 | 136·157 45 | 11·045 | 83 | 37·574 | 121 | 79·854 | 159 | 137·886 46 | 11·541 | 84 | 38·485 | 122 | 81·180 | 160 | 139·626 47 | 12·048 | 85 | 39·406 | 123 | 82·516 | 161 | 141·377 —————+—————————+———————+—————————+———————+—————————+———————+————————

[Pg521] The practical application of the preceding formulæ will be shown by the following examples.

EXAMPLES.

1. _A 36-inch cylinder with 5-1/2 feet stroke is supplied by a boiler evaporating effectively 60 cubic feet of water per hour, and the piston makes 20 strokes per minute without expansion;-- what is the power of the engine and the pressure of steam in the cylinder?_

Let it be assumed that r = 6 × 144 = 864 and m = 0·1. Since the engine is a condensing engine, we have b = 164 and e′ = 3691399. By the formulæ (25.) and (26.) we have

H = [We′ − VA(b + r)]/[33000(1 + m)];

and since by the data we have

W = 1 A = 7·069 V = 2nL = 40 × 5·5 = 220,

the formula, by these substitutions, becomes

H = (3691399 − 220 × 1028 × 7·069) / (33000 × 1·1); ∵ H = 57·6.

Since e = 1, the pressure P of steam in the cylinder, by (18.), is

P = (We′/VA) − b.

Therefore

P = (3691399/1555·18) − 164 = 2210;

which being the pressure in pounds per square foot, the pressure per square inch will be 15-1/3 lbs.

2. _To find the effective evaporation necessary to produce a power of 80 horses with the same engine. Also, find the pressure of steam in the cylinder, the speed of the piston being the same._

By the formula (32.), with the above substitutions, we have

W = (33000 × 80 × 1·1 + 220 × 7069 × 1028)/3691399 = 1·22.

The evaporating power would therefore be only increased 22 per cent., while the working power of the engine would be increased nearly 40 per cent.

The pressure P in the cylinder will be given, by (18.), as before.

P = [(1·22 × 3691399)/1555·18] − 164 = 2732;

which is equivalent to 19 lbs. per square inch. [Pg522]

3. _What must be the diameter of a cylinder to work with a power of a hundred horses, supplied by a boiler evaporating effectively 70 cubic feet of water per hour, the mean speed of the piston being 240 feet per minute, and the steam being cut off at half stroke? Also, what will be the full pressure of steam on the piston?_

Taking, as in the former examples, m = 0·1, b = 164, and r = 864, we shall have

H = 100 W = 7/6 V = 240,

and by the column for condensing engines, in table, p. 519, we have e′ = 6029916, where e = 0·50. Making these substitutions in

We′ = 33000 H (1 + m) + VA (b + r),

we shall have

(7/6) × 6029916 = 3300000 × 1·1 + 240 × 1028 × A.

Whence we find

A = 13·8;

and by the table, p. 520, the corresponding diameter of the cylinder will be 50-1/3 inches.

If P′ be the full pressure of the steam, we shall have, by (18.),

P′ = (Wa/VA(e + c)) − b.

Making in this the proper substitutions, we have

P′ = ((7/6) × 3875969) / (240 × 13·8 × 0·55) − 164 = 2318;

which being in pounds per square foot, the pressure per square inch will be 16-1/10 lbs.

FOOTNOTES:

[40] M. de Pambour states that the increased volume is 1364 cubic inches.

[41] Formulæ equivalent to some of the preceding are given, with numerous others, by M. de Pambour, in his Theory of the Steam Engine. These mathematical details contain nothing new in principle, being merely the application of the known principles of general mechanics to this particular machine. M. de Pambour objects against the methods of calculating the practical effects of steam engines generally adopted by engineers in this country. Their estimates of the loss of power by friction, imperfect condensation, and other causes, are, as I have stated in this volume, vague, and can be regarded at best as very rough approximations; but, subject to the restrictions under which their methods of calculation are always applied, they are by no means so defective as M. de Pambour supposes. He proves what he considers to be their inaccuracy, by applying them in cases in which they are never intended to be applied by English engineers. Those who desire to reduce to general algebraical formulæ the effects of the different kinds of steam engines will, however, find the volume of M. de Pambour of considerable use.

[Pg523]

INDEX.

Air, elasticity of, 28; May be partially expelled from a vessel by the application of heat, 44.

America, steam navigation first established in, 487; Circumstances which led to it, 488; Fitch and Rumsey, their attempts to apply the single-acting engine to the propulsion of vessels, 489; Stevens of Hoboken commences experiments on steam navigation, 489; Experiments of Livingstone and Fulton, 489; Fulton's first boat, 490; The Hudson navigated by steam, 491; Extension and improvement of river navigation, 492; American steamers, 494; Difference between them and European steamers, 494; Steamers on the Hudson, 494; American paddle-wheels, 495; Sea-going American steamers, 496; Speed attained by American steamers, 497; Lake steamers, 499; The Mississippi and its tributaries, 499; Steam-boats navigating it, 500; Their structure and machinery, 500; New Orleans Harbour, 503; Steam tugs, 503.

Atmosphere, 38; Weight of, 39.

Atmospheric air, mechanical properties of, 38; Composition of, 253.

Atmospheric engine, Thomas Newcomen the reputed inventor of, 62; Description of, as first constructed by Newcomen, 67; The operation of considered, 69; Not unfrequently used in preference to the modern steam engine, 72; Advantages which it possessed over Savery's, 73; Considerably improved by Beighton, 75; John Smeaton investigates this machine, 76; Brindley obtains a patent for improvements in, 76; Applied by Champion of Bristol to raise water, 181; Possessed but limited power of adaptation to a varying load, 151; Expedient to remedy this, 151; Working-beam, cylinder, and piston applied to by Newcomen, 322.

Atmospheric pressure rendered available as a mechanic agent by Denis Papin, 38; Means of measuring the force of, 39; The idea of using against a vacuum or partial vacuum to work a piston in a cylinder, suggested by Otto Guericke, 73.

Barometer gauge, 272.

Barton's piston, 248.

Beighton, his improvement of the atmospheric engine, 75.

Black, Dr., his doctrine of latent heat, 93.

Blasco de Garay, his contrivance to propel vessels, 16; The contrivance of, probably identical with that of Hero, 17.

Blinkensop, his locomotive engine, 337.

Blowing-box, 429.

Blowing out, Seaward's method of, 454.

Blow-off cocks, 452.

Boiler, forms of, most convenient, 255; The waggon boiler adopted by Watt, 255; Furnace, 256; Method of feeding, 257; Combustion of gas in flues, 260; Mr. Williams's method of consuming the unburned gases which escape from the grate, and are carried through the flues, 260; Construction of grate and ash-pit, 261; Magnitude of heating surface of boiler, 262; Capacity of, must be proportioned to the quantity of water to be evaporated, 263; Water-space and steam-space in boiler, 263; Proportion of water-space in the boiler, how to be regulated, 264; Position of flues, 264; Method of feeding, 265; The magnitude of the feed should be equal to the quantity of water evaporated, 265; Different methods for indicating the level of the water in the boiler, 266; Level guages, 266; Self-regulating feeder, 267; Another method of arranging, 269; Steam gauge, 270; Thermometer gauge, 271; Barometer gauge, 272; The indicator to measure the mean efficient force of the piston invented by Watt, 274; The counter contrived by Watt, 278; Safety valve, 279; Fusible plugs used in high pressure boilers, 280; Self-regulating damper, 281; Self-regulating furnace invented by Brunton, 283; Duty of a boiler, 294; Boilers of locomotive engines, 351; Construction of the boiler of Gurney's steam carriage, 423; All boilers require occasional cleansing, 427; Gurney's method of removing crust of deposited matter in boilers, 427; The boiler of Dr. Church's engine formed of copper, 439; Boilers in marine engines, 449; Effects of sea-water in, 450; Remedies for them, 451; Substitution of copper for iron, 460; Expedient of coating boilers with felt, applied by Watt, 463.

Booth, Mr., his report on locomotive engines, 361.

Boulton and Watt's experiments on the horse power of engines, 288.

Branca, Giovanni, his machine for propelling a wheel by a blast of steam, 22.

Brindley (James) obtains a patent for improvements in atmospheric engine, 76; Undertook to erect an engine at Newcastle-under-Lyne, 76; Discouraged by the obstacles thrown in his way, 76.

Brougham, Lord, his sketch of Watt's character, 313; Inscription from the pen of, on Watt's monument in Westminster Abbey, 320.

Buffers, 404.

Cartwright's engine to use the vapour of alcohol to work the piston, 245; His piston, 247.

Cawley and Newcomen obtain a patent for the atmospheric engine, 64.

Champion applies atmospheric engine to raise water, 181.

Chapman, Messrs., their locomotive engine, 337.

Chlorine introduced in bleaching by Watt, 310.

Church, Dr., his steam engine, 439; The boiler formed of copper, 439.

Coals, the virtues and powers which steam has conferred upon, 6; The amount of labour a bushel of performs by means of the steam engine, compared with horse power, 7; Constituents of, 252; Process of combustion, 252.

Coal mines, apprehensions as to the possibility of the exhaustion of groundless, 8.

Cocks, friction on, 240.

Cocks and valves, 227.

Combustion of gas in flues, 260.

Condensation by injection, accidental discovery of, 69.

Condensation in the cylinder incompatible with a due economy of fuel, 120.

Condensing principle, circumstance which led to Savery's discovery of, 47.

Condensing pipe in Savery's engine, 52.

Condensing out of the cylinder, 120.

Condensing jet, 191.

Conical steam valves, 228.

Conversion of ice into water, 103; Of water into steam, 105.

Copying press invented by Watt, 302.

Cornish system of inspection, 297.

Cornish engines, improvement of, 298; Historical detail of the duty of, 299.

Cylinders, Wilkinson's machine for accurately boring the insides of, 149.

D valve, 230.

Dalton and Gay-Lussac, law of, relating to the pressure of elastic bodies, 171.

Dixon, Mr. The substitution of brass for copper tubes in locomotive engines ascribed to him, 370.

Double clack-valve, 228.

Eccentric, 225; Two expedients to reverse the position of, 379.

Effect of an engine, 285.

Elastic fluids. The law according to which the pressure of, increases with their temperature, discovered by Dalton and Gay-Lussac, 171.

Evaporation of water and other liquids, physical and mechanical principles connected with, 97.

Expansion of common steam, effects of, 173.

Expansive action of steam, 159; Stated by Watt in a letter to Dr. Small, 157; Its principle explained, 158; Mechanical effect resulting from it, 161; Computed effect of cutting off steam at different portions of the stroke, 162; Involves the condition of a variation in the intensity of the moving power, 163; Expedients for equalising the power, 164; The expansive principle in the engines constructed by Boulton and Watt, limited, 165; Its more extensive application in the Cornish engines, 165; Methods of equalising, 174; Description of Hornblower's engine for this purpose, 174.

Expansive principle, application of in marine engines, 466.

Farey on the steam engine, quotation from, relative to Savery's engine, 58; His evidence before the House of Commons, 435.

Field, construction of his split paddle, 478.

Fitch and Rumsey, their attempts to apply the single-acting engine to the propulsion of vessels, 489.

Flues, position of, 264.

Fluids, of two kinds, 25; Mechanical properties of, 25; Elastic, 27; Experimental proof that they press equally in all directions, 41.

Fly-wheel, 205.

Four-way cock, 239; Disadvantages of, 240.

Fuel, means of economising, in marine furnaces, 463.

Fulton and Livingstone, their experiments in steam navigation, 489.

Fulton's first boat, 490.

Furnace, self-regulating, invented by Brunton, 283.

Fusible plugs used in high-pressure boilers, 280.

Galloway, his paddle-wheel described, 476.

Gas, elasticity of, 28.

Gay-Lussac and Dalton, law of, relating to the pressure of elastic bodies, 171.

Governor, adaptation of, 209.

Gradients, restrictions on, 411; Disposition of, should be uniform, 415.

Great Western Railway, Dr. Lardner's experiments on, 408.

Griff, proposals to drain a colliery at, mentioned by Desaguliers, 64.

Gurney's steam carriage, 423; Construction of the boiler of, 423; His method of removing crust of deposited matter in boilers, 427; His experiments on common roads, 432.

Hall, his condensers described, 458.

Hancock, his steam carriage, 436; In what manner it differs from that of Gurney, 437.

Harris, Dr., mentions Savery's engine in his "Lexicon Technicum," 56.

Heat, effects of upon water, 29; Waste of in atmospheric engine, 89; An examination of the analogous effects produced by the continued application of, to water in the liquid state, 102; Radiation of, 254.

Heating by steam brought forward by Watt, 303.

"Hecla," experiments with the, 412.

Hero of Alexandria, description of his machine, 12.

High pressure engines described, 321; One of the earliest forms of the steam engine, 322; Obscurely described in the "Century of Inventions," 322; Construction of the first, by Messrs. Trevethick and Vivian, 324.

Hooke exposes the fallacy of Papin's project, 64.

Horse carriages compared with steam, 435.

Horse power of steam engines, 288; Smeaton's estimation of, 288; Boulton and Watt's experiments on, 288.

Howard's description of his marine engine, 464.

Hudson, the, navigated by steam, 491.

Hull, Jonathan, his application of the steam engine to water wheels, 180.

Humphrey. His marine engine described, 470.

Huskisson, Mr., death of, 329.

Hydrogen, 253.

India, steam navigation to, 483.

Indicator invented by Watt, 274.

Jeffrey, Lord; his sketch of the character of Watt, 315.

Kinneal, description of Watt's experimental engine at, 131.

Lake steamers, 499.

Lardner's, Dr., experiments on the Manchester Railway in 1832, 357; His experiments in 1838, 406; Experiments on the Great Western Railway, 408.

Leupold's engine, description of, 323.

Level gauges, 266.

Linen, machine for drying by steam, invented by Watt, 303.

Liverpool and Manchester railroad, effects of the introduction of steam transport on, 329; Want of experience in the construction of the engines, 329; Death of Mr. Huskisson, 329; Proceedings of the directors, 342; Premium offered by them for the best engine, 344; Experimental trial, 344.

Livingstone and Fulton, experiments of in steam navigation, 489.

Locomotive engine, history of, 328; Blinkensop's engine, 337; Chapman's engine, 337; Walking engine, 337; Mr. Stephenson's engine at Killingworth, 339; Defect of, 341; Description of the "Rocket," 345; The "Sanspareil," 347; The "Novelty," 349; Superiority of the "Rocket," 350; Subsequent improvements in the locomotive engine, 352; Table, showing the economy of fuel gained by subdividing the flue into tubes, 354; Engines constructed in the form of the "Rocket" subject to two principal defects, 354; These defects remedied, 355; Improved by the adoption of a more contracted blast pipe, 356; Dr. Lardner's experiments in 1832, 357; Adoption of brass tubes, 361; Mr. Booth's report, 361; Detailed description of the most improved locomotive engines, 364; Substitution of brass for copper tubes ascribed to Mr. Dixon, 370; Mr. Stephenson constructed the driving wheels without flanges, 383; Pressure of steam in the boiler limited by two safety- valves, 402; Buffers, 404; Steam whistle, 404; Water tank, 404; Power of locomotive engines, 405; Evaporation of boilers, 406; Dr. Lardner's experiments in 1838, 406; Resistance to railway trains, 407; Dr. Lardner's experiments on the Great Western Railway, 408; Restriction on gradients, 411; Experiment with the "Hecla," 412; Disposition of gradients should be uniform, 415; Method of surmounting steep inclinations, 415; Steam carriages on common roads, 419; Difference between steam engines on railways and those used to propel carriages on turnpike roads, 422; Gurney's steam carriage, 423; Construction of the boiler of, 423; Escape of steam from the engines on the Liverpool road, 428; Blowing-box, 429; Separator, 430; Difficulties in the practical working of steam carriages upon common roads, 432; Gurney's experiments on common roads, 432; Prejudice against locomotive engines on common roads, 432; Not more destructive to roads than carriages drawn by horses, 433; Report of the committee of the House of Commons, 433; Weight of steam carriages, 433; Two methods of applying locomotives upon common roads, 434; Horse carriages compared with, 435; Farey's evidence before the House of Commons, 435; Risk of accident from explosion extremely slight, 435; Hancock's steam carriage, 436; In what manner it differs from that of Gurney, 437; Ogle's steam carriage, 438; His evidence before the House of Commons, 439; Dr. Church's steam engine, 439; The boiler of formed of copper, 439.

Lunar Society, Boulton and Watt leading members in, 302.

Marine engines, form and arrangement of, 441; Difference between marine and land engines, 443; Engine-room, arrangement of, 446; Boilers in, 449; Effects of sea-water on boilers, 450; Remedies for them, 451; Blow-off cocks, 452; Indicators of saltness, 452; Seaward's indicator, 454; His method of blowing out, 454; Method of Maudslay and Field to preserve freshness of water in the boiler, 456; Brine pumps, 457; Tubular condensers applied by Mr. Watt, 457; Hall's condensers, 458; Substitution of copper for iron boilers, 461; Process of stoking, 462; Marine furnaces, 463; Expedient of coating boilers with felt applied by Watt, 463; Means of economising fuel, 463; Description of Howard's engine, 464; Application of the expansive principle in marine engines, 466; Recent improvements of Messrs. Maudslay and Field, 467; Humphrey's engine, 470; Common paddle-wheel, 472; Defect of, 474; Feathering paddles, 474; Galloway's paddle-wheel, 476; Field's split paddle, 478; Proportion of power to tonnage, 480; Iron steam vessels, 482.

Mariotte's law relating to pressure, 171.

Maudslay and Field, their method to preserve the requisite freshness of water in the boiler, 456; Brine pumps, 457; Recent improvements of in marine engines, 466.

Metallic pistons, 244; Cartwright's engine, 245; An improved form given to by Barton, 248.

Mill work, Stewart's application of the steam engine to, 182.

Mines, the drainage of, Watt endeavours to bring to perfection the application of the steam engine to, 178.

Mississippi and its tributaries, 499; Steam-boats on, 500; Their structure and machinery, 500.

Morland, Sir Samuel, his application of steam to raise water, 34; The reputed inventor of several ingenious contrivances, 34; His work in French upon the raising of water, 35; Extract from it, 35; Evelyn's account of his visit to, 36.

Murray's slide-valve, 229.

Newcomen, Thomas, the reputed inventor of the atmospheric engine, 62; His acquaintance with Dr. Hooke, 62; Acquainted with Papin's writings, 64; The merits of his engine ascribed principally to its mechanism and combinations, 73; Obtains with Cawley a patent for the atmospheric engine, 64; Resumes the old method of raising water from mines by ordinary pumps, 65; The means proposed to effect this, 66; First conception of the atmospheric engine, 66; Description of his construction of atmospheric engine, 67; Suggestion of a better method of condensation than the application of cold water on the external surfaces of the cylinder, 69; He abandons the external cylinder, 69; Applied the working-beam, cylinder, and piston to the atmospheric engine, 322.

New Orleans Harbour, 503.

"Novelty," description of the, a locomotive engine, 349.

Ogle, his steam carriage, 438; His evidence before the House of Commons, 439.

Otto Guericke, his suggestion relative to atmospheric pressure, 73.

Oxley made the first attempt to drive water-wheels by the steam engine, 182.

Paddle-wheel described, 472; Defect of, 474; Feathering paddles, 474; Galloway's paddle-wheel, 476; Field's split paddle, 478.

Paddle-wheels of American steamers, 495.

Papin, Denis, conceived the idea of rendering atmospheric pressure available as a mechanical agent, 37; Description of his contrivance, 37; His discovery of condensation of steam, 45; Quotation from his work relative to this discovery, 45; Explanation of this important discovery, 46; Discovers the method of producing a vacuum by the condensation of steam, 178; His projected applications of the steam engine, 178; His proposition for the construction of an engine working by atmospheric pressure, 62; Abandons the project when informed of the principle and structure of Savery's engine, 62; His engine described, 62; This project nothing more than a reproduction of the Marquis of Worcester's engine, 63; The fallacy of his project exposed by Hooke, 64; His project for producing a vacuum under a piston by condensing the steam, published in the "Actæ Eruditorum," 64.

Parallel motion, 195.

Physical science, the rapid progress of, 8.

Pistons, 242; The common hemp-packed, 242; Woolf's method of tightening the packing of, without removing the lid of the cylinder, 244; This method further simplified, 244; Metallic, 244; Cartwright's engine, 245; Cartwright's piston, 247; Invention of the indicator by Watt to measure the mean efficient force of, 274.

Piston rod and beam, methods of connecting in the double-

## acting engine, 193.

Pneumatic institution at Clifton, Watt one of the founders of, 310.

Potter, Humphrey, his contrivance for working the valves, 71; Improved by the substitution of a plug-frame, 72.

Power, proportion of, to tonnage in marine engines, 480.

Power and duty of steam engines, 287.

Priestley, Watt's letter to, relative to the composition of water, 307.

Pump, an illustration of force attained by a vacuum, 43.

Puppet clacks, or button valves, 144.

Rack and Sector, 194.

Railways, speed of coaches on, compared with that of stage- coaches on a common road, 7.

Railway transport, effects of, 328. 330.

Railways and stone roads compared, 420.

River navigation, extension and improvement of, 492.

"Rocket," description of the, a locomotive engine, 345; Engines constructed in the form of, subject to two principal defects, 354; These defects remedied, 355; Improved by the adoption of a more contracted blast-pipe, 356.

Roebuck, Dr., Watt's partnership with, 130.

Rotatory motion, method of producing by sun and planet wheels, 187.

Safety-valve not adopted by Savery, 57; Invented by Papin, 57; Description of, 57; First applied to Savery's engine by Desaguliers, 58.

"Sanspareil," description of the, a locomotive engine, 347.

Savery, Thomas, obtains a patent for an engine to raise water, 47; Circumstance which led to his discovery of the condensing principle, 47; An account of his engine, 49; Description of the working apparatus in which the steam is used as a moving power, 51; His engine described in a work entitled "The Miner's Friend," 56; Mentioned by Dr. Harrison in his "Lexicon Technicum," 56; Quotation from his address to the Royal Society, 56; Quotation from his address to the Miners of England, 57; Mentioned by Bradley in his "Improvements of Planting and Gardening," 57; The safety-valve not adopted by him, 57; The safety-valve first applied to his engine by Desaguliers, 58; Farey on the steam engine quoted, 58; Further Improvements made by Desaguliers, 58; Defects of his engine, 59; His engine applied to the drainage of mines, 59; Further defects of, 60; The first to suggest the method of expressing the power of an engine with reference to that of horses, 61; Failure of his engine in the work of drainage, 61; The tendency of high pressure to weaken and gradually destroy the vessels, 72; The power of his engines restricted, 73; The atmospheric engine superior to, 73; The boiler, guage-pipes, and regulator borrowed from his engine, 73; Proposes to apply his engine as a prime mover for all sorts of machinery, 180.

Scott, Sir Walter, his sketch of the character of Watt, 314.

Sculpture, Watt's invention of machine for copying, 318.

Sea-going American steamers, 496.

Sea-water, effects of upon boilers, 450.

Seaward's slides, 235; Indicator of saltness, 454; His method of blowing out, 454.

Self-regulating damper, 281; Furnace, 283.

Separator, 430.

Single-acting engine, description of Watt's, 133. 144.

Single clack-valve, 227.

Single cock, 238.

Slide-valves, 229; That contrived by Mr. Murray, 229.

Smeaton, John, investigates the atmospheric engine, 76; Applies himself to the improvement of wind and water mills, 181; His estimate of the horse power of engines, 288.

Solomon De Caus, description of the apparatus of, 17; M. Arago claims for him a share of the honour of the invention of the steam engine, 21; Republished, with additions, the work of Isaac De Caus, 22.

Somerset, Edward, Marquis of Worcester. Invention of the steam engine ascribed to him, 23; Description of his contrivance, 23; His "Century of Inventions," 24; Brief account of his engine described in this work, 31; His contrivance compared with that of De Caus, 33; Many of his inventions have been reproduced and brought into general use, 34.

Steam cannot be applied _immediately_ to any useful purpose, but requires the interposition of mechanism, 11; Elastic force of, recognised by the ancients only in vague and general terms, 14; The power of, formerly made to minister to the objects of superstition, mentioned by Arago, 15; Anecdote showing the knowledge which the ancients had of the mechanical force of, 15; The discovery of the condensation of, by Papin, 45; Mechanical power obtained from the direct pressure of the elastic force of, suggested by De Caus and Lord Worcester, 73; Latent heat of, 107; The mechanical force of considered, 115; Watt's early experiments on, 87; Discovery of the expansive action of, 157; Expansive action of stated by Watt in a letter to Dr. Small, 157; Its principle explained, 158; Mechanical effect resulting from it, 161; Properties of, 168; Common and super-heated steam, 168; Pressure and temperature of, 171; Relation between the temperatures of common steam and its pressure and density, 172; Effects of the expansion of common steam, 173; Mechanical effects of, 173; Methods of equalising the varying force of expanding steam, 174; Method of producing a vacuum by the condensation of, discovered by Papin, 178; Applied to move machinery, 179; Steam guage, 270; Heating by steam brought forward by Watt, 303; A machine for drying linen by, invented by Watt, 303; Mode of escape of, from the engines on the Liverpool road, 429.

Steam case or jacket, invented by Watt, 124.

Steam engine, a subject of popular interest, 3; The effects which it has produced upon the well-being of the human race considered, 4; Presents peculiar claims upon the attention of the people of Great Britain, 5; The exclusive offspring of British genius, 5; The virtues and powers which it has conferred upon coals, 6; Water the means of calling these powers into activity, 6; Used in the drainage of Cornish mines, 7; Comparison of its power with human labour, 8; Investigation of the origin of, 10; A combination of a great variety of contrivances and the production of several inventions, 12; Before the discoveries of James Watt was of extremely limited power, 12; Invention of, ascribed to the Marquis of Worcester, 23; Account of Savery's, 49; Farey quoted, 58; Improvements made by Desaguliers, 58; Applied to the drainage of mines, 59; Humphrey Potter's contrivance, 72; Advantages of the atmospheric engine over that of Savery, 73; Progress of the atmospheric engine, 75; Description of Papin's engine, 62; Smeaton's improvements, 76; First experiments of Watt and subsequent improvements, 83; Watt's experiments on the force of steam at high pressure, 83; Watt discovers the great defects of the atmospheric engine, 85; Waste of heat in atmospheric engine, 89; Dr. Black's theory of latent heat, 93; Description of Watt's experimental engine at Kinneal, 131; Description of his single-acting engine, 133; Disadvantages of the atmospheric compared with the old engine, 150; Expedients to force the atmospheric engines into use, 152; Watt's exertions to improve the manufacture of, at Soho, 155; Efficiency of fuel in the new engines, 156; Hornblower's engine, 175; Woolf's engine, 176; Watt endeavours to bring to perfection the application of, to the drainage of mines, 178; Papin's projected application of, 178; Savery proposed to apply his steam engine as a prime mover for all sorts of machinery, 180; Jonathan Hull's application of, to water-wheels, 180; Steam engine used for driving water wheels, 182; First attempt of this kind made by Oxley, 182; Stewart's application of, to mill work, 182; Wasbrough's application of the fly-wheel and crank, 183; Reasons why Watt's single-acting engine was not adapted to produce continuous uniform motion of rotation, 184; Watt's second patent, 186; Valves of double-acting engine, 189; Condensing jet, 191; Methods of connecting the piston-rod and beam in the double-

## acting engine, 193;

Rack and sector, 194; Parallel motion, 195; Connecting rod and crank, 202; Fly-wheel, 205; Throttle-valve, 207; Adaptation of the governor, 209; Double-acting engine considered as a whole, 216; Process of its operation investigated, 217; The eccentric, 225; Cocks and valves, 227; Single clack-valve, 227; Double clack-valve, 228; Conical steam-valves, 228; Slide-valves, 229; Murray's slide-valve, 229; D valve, 230; Seaward's slides, 235; Single cock, 238; Four-way cock, 239; Pistons, 242; Gross effect and useful effect of engines, 285; Power and duty of, 287; Horse power of, 288; The means whereby mechanical power is expended in working the engines enumerated, 290; Common rules followed by engine makers, 292; Duty of engines, 294; Duty distinguished from power, 295; Proportion of stroke to diameter of cylinder, 295; Cornish system of inspection, 297; Improvement of the Cornish engines, 298; Historical detail of the duty of Cornish engines, 299; High-pressure engines, 321; Leupold's engine described, 323; Construction of the first high-pressure engine by Messrs. Trevethick and Vivian, 324; First application of the steam engine to propel carriages on railroads, 328; Computation of how much corn could be saved by the substitution of steam engines for horse power, 332; Marine engines, form and arrangement of, 441; Difference between marine and land engines, 443; Mr. Howard's patent engine described, 464; Humphrey's engine described, 470.

Steam navigation to India, 483; First established in America, 487; Circumstances which led to it, 488; Attempts of Fitch and Rumsey to apply the single-acting engine to the propulsion of vessels, 489; Stevens of Hoboken commences experiments in, 489; Experiments of Livingstone and Fulton, 489; Fulton's first boat, 490; The Hudson navigated by steam, 491; Extension and improvement of river navigation, 492; American steamers, 494; Difference between them and European steamers, 494; Steamers on the Hudson, 494; Sea-going American steamers, 496; Speed attained by American steamers, 497; Lake steamers, 499; Steam-boats on the Mississippi, 500.

Steam tugs, 503.

Steep inclinations, method of surmounting, 415.

Stephenson, his locomotive engine at Killingworth, 339; Defect of, 341; Constructed the driving wheels without flanges, 383.

Stevens, of Hoboken, commences experiments on steam navigation, 489.

Stewart, his application of the steam engine to mill work, 182.

Stoking, process of, 462.

Stuffing-box, contrivance of, 147.

Sun and planet wheels, method of producing rotatory motion, 187.

Thermometers, the process of filling described, 44; Explanation of the principle of, 98; Construction of mercurial thermometer, 98; Method of graduating, 99.

Thermometer gauge, 270.

Throttle-valve, description of, 207.

Tredgold, his remark relative to Newcomen's engine, 73.

Trevethick and Vivian's engine described, 325.

Vacuum, force obtained by a, 43; The pump an illustration of this, 43.

Valves of double-acting engine, 189.

Wasbrough, his application of the fly-wheel and crank, 183.

Water, a pint of, the mechanical force produced by its evaporation, 6; The alternate decomposition and recomposition of, by magnetism and electricity, analogous to vaporisation and condensation, 8; The fixed temperature which it assumes in boiling subject to variation, 108; Experiments to illustrate this, 109; Table to show the temperature at which it will boil under different pressures of the atmosphere, 113; Mechanical force of a cubic inch of, converted into steam, 118; Discovery of the composition of, 303; The merit of this discovery shared between Cavendish, Lavoisier, and Watt, 305; Latent heat of, 101; Conversion of ice into, 103.

Water tank, 404.

Water-wheels, steam engine used for turning, 182.

Watt (James), birth of, 77; His infancy, 78; Anecdotes respecting, 78; His boyhood, 79; Goes to London, 80; Returns to Glasgow, 80; Appointed mathematical instrument-maker to the university, 81; Adam Smith one of his earliest friends and patrons, 81; Also Black and Robert Simson, 81; Extract from an unpublished manuscript of Robison respecting the character of, 82; His first experiments on steam, 83; Observes defects of atmospheric engine, 84; His first attempt to improve it, by using a wooden instead of an iron cylinder, 85; His method to ascertain the temperatures at which water would boil under pressures less than that of the atmosphere, 86; His early experiments on steam, 87; His notice of the waste of heat in atmospheric engines, 89; His experiments to determine the extent to which water enlarged its volume when it passed into steam, 90; Discovers the latent heat of steam, 91; Learns the theory of latent heat, 93; His letter to Dr. Brewster, explaining the circumstances which led to the error that a large share of the merit of his discoveries were due to Black, 93; Finds that condensation in the cylinder is incompatible with a due economy of fuel, 120; Conceives the notion of condensing out of the cylinder, 120; Discovers separate condensation, 121; Invents the air-pump, 122; Substitutes steam pressure for atmospheric pressure, 123; Invents the steam case or jacket, 124; His first experiments to realise these inventions, 125; His experimental apparatus, 126; Difficulties of bringing the improved engines into use, 128; Practises as a civil engineer, 129; Makes a survey of the river Clyde, 129; His partnership with Dr. Roebuck, 130; His first patent, 130; Description of his experimental engine at Kinneal, 131; Removes to Soho, 131; Abstract of the act of parliament for the extension of his patent, 132; Description of his single-acting engine, 133-144; His condenser worked by an injection, 146; Objections attending condensation by surface, 146; Improvements in construction of piston, 147; Effected by a contrivance called a stuffing-box, 147; Method of packing, 148; Improved methods of boring the cylinder, 149; His letter to Smeaton on this subject, 149; Used black-lead dust for the purpose of lubrication, 149; This found to wear the cylinder, 149; Disadvantages of the atmospheric compared with the old engines, 150; Greatly increased economy of fuel, 151; Expedients to force the atmospheric engines into use, 152; His correspondence with Boulton, 153; His correspondence with Smeaton, 154; Exertions to improve the manufacture of engines at Soho, 155; Efficiency of fuel in the new engines, 156; Endeavours to bring to perfection the application of the steam engine to the drainage of mines, 178; The reasons why his single-acting engine was not adapted to produce continuous uniform motion of rotation, 184; His notes upon Dr. Robison's article on the steam engine, 184; His second patent, 186; His third patent, 189; His application of the fly-wheel, 205; His application of the throttle-valve, 207; His adaptation of the governor, 209; His double-acting engine considered as a whole, 216; Investigation of the process of its operation, 217; Eccentric, 225; Cocks and valves, 227; Single clack-valve, 227; Double clack-valve, 228; Conical steam-valve, 228; Slide-valves, 229; The waggon boiler adopted by him, 225; Invents the indicator, 274; The counter contrived by him, 278; The Lunar Society in which Watt and Boulton were leading members, 302; Invents the copying press, 302; His friends and associates at Birmingham, 302; Method of heating by steam brought forward by him, 303; His invention of a machine for drying linen by steam, 303; His share in the discovery of the composition of water, 303; His letter to Priestley on this subject, 307; Anecdote of his inventive genius, 309; Introduces the use of chlorine in bleaching, 310; One of the founders of the Pneumatic institution at Clifton, 310; His first marriage, 310; Private life of, 311; Death of his first wife, 311; His second marriage, 311; He retires from business, 311; Death of his younger son, 311; Extracts from his letters, 312; His death, 313; Character of, by Lord Brougham, 313; By Sir Walter Scott, 314; By Lord Jeffrey, 315; Occupation of his old age, 318; Invention of machine for copying sculpture, 318; His last days, 318; Monuments, 319; Inscription on the monument in Westminster Abbey from the pen of Lord Brougham, 319; His application of tubular condensers, 457; His expedient for coating boilers with felt, 463.

Wilkinson, his machine for accurately boring the insides of cylinders, 149.

Williams's method of consuming the unburned gases which escape from the grate, and are carried through the flues, 260.

Woolf's engine, 176; Woolf's piston, 243.

[Illustration: RICHMOND BRIDGE.]

LONDON:

Printed by A. SPOTTISWOODE, New-Street-Square.

* * * * *

Transcriber's endnote:

Original spelling and grammar has mostly been retained. For example, the forms "Cyclopoedia", "cyclopædia", "Encyclopædia", "Encyclopoedia", "guage", and "gauge" are all retained. Figures were moved from within paragraphs to between paragraphs. Footnotes were re-indexed and moved to the ends of chapters.

An entry for the INDEX was inserted into the Table of Contents.

In the Table of Contents, changed "MM. Dulong and Arrago" to "MM Dulong and Arago". Also "Blinkinsop" to "Blinkensop". Also "Wasborough's" to "Wasbrough's".

Figs. 4, 5 and 6 are all in one image. Two tubes in Fig. 4 were incorrectly labeled T'; one of these has been crossed out and changed to T. Both tubes in Fig. 6 were incorrectly labeled G. One of these was crossed out and replaced by G'. Note also that Figs. 4, 5, 6 are repeated in the text on different pages; this feature has been retained.

Page 10: "it s already" to "it is already".

Page 43: "Thu if heat" changed to "Thus if heat".

Page 45: "had a diameter of only one square foot" changed to "had a diameter of only one foot".

Page 47: "immedate" to "immediate".

Page 51: "a a level" to "a level". Also, comma removed from "A gauge, pipe is inserted".

Page 53: "proportionably" to "proportionally".

Page 79: A paragraph beginning "He was not fourteen" contains three double quotation marks; this is presumably an error. Possibly there should be two double quotation marks and two single quotation marks.

Page 80: "S'. Gravesande" is retained, although this probably refers to a person known as "'s Gravesande".

Page 103: "gases n general" to "gases in general".

Page 122: comma removed from "process may, be continued".

Page 123: "two thin pipes F G of tin" to "two thin pipes F, G of tin".

Page 172: "empyrical" to "empirical".

Page 187, Fig. 32.: The text refers to "end I of the connecting rod", but this was labeled L on the Figure. This L has been crossed out and replaced by I.

Page 285: In "surrounding the boiler with iron-conducting substances", changed "iron-" to "non-".

Page 308: "exeitement" to "excitement".

Page 362: "acomplish" to "accomplish".

There were several extended quotations, for example beginning on page 312, in which each line began with a quotation mark, with ending quotation marks at the end of each paragraph. In this edition, these passages have been marked by indentation, and all but the first and last quotation marks from each paragraph were removed.

Page 366: Figs. 97-104 appeared originally between pages 385 and 399, as full-page prints. Numerically, however, they belong between Figs. 96 and 105--therefore between pages 366 and 369. Therefore, they have been moved to a location between two paragraphs on page 367.

Page 368: "rivetted" to "riveted".

Page 419: "TREVITHECK'S INVENTION" changed to "TREVETHICK'S INVENTION", in the chapter heading. However, the references to Trevethick occur in a previous chapter, around page 324.

Page 468: Period added to end sentence "[...] piston is at the bottom of its stroke".

Page 490: Period added to end sentence "[...] therefore one eighth of its capacity".

Pages 494, 497: large data tables were split into two pieces each.

Page 505: The logarithm originally given as log x = "[=1]·82340688193", where "[=1]" represents a numeral one with a horizontal line over it, is herein changed to log x = "0·82340688193 - 1", as that is the meaning of this convention.

Page 513 "formulæ are hyberbolic" to "formulæ are hyperbolic".

In the Appendix, pp 505-522, mathematical variables such as "a", "p", "t", etc. were originally italicized. In these text file versions, italicized variables have been removed from this section of the book. This rule has two unfortunate exceptions: E, _E_, E', and _E'_ on pp 512-515 are different variables, and have been retained. Italics have been removed from tables throughout the work.

The tables on page 494 and 497 were divided into two parts, better to fit the width constraints of this format. Most of the tables will not look good unless viewed with a monospace font, such as Courier New or Lucida Console.