Part 9

In many cases the experiments have not shown a change at all in the plane of oscillation of the pendulum; in others the alteration in the plane of vibration has been in the _wrong direction_; and very often the _rate of variation_ has been altogether different to that which theory indicated. The following is a case in illustration:--“On Wednesday evening the Rev. H. H. Jones, F.R.A.S., exhibited the apparatus of Foucault to illustrate the diurnal rotation of the Earth, in the Library Hall of the Manchester Athenæum. The preparations were simple. A circle of chalk was drawn in the centre of the floor, immediately under the arched skylight. The circle was exactly 360 inches in its circumference, every inch being intended to represent one degree. According to a calculation Mr. Jones had made, and which he produced at the Philosophical Society six weeks ago, the plane of oscillation of the pendulum would, at Manchester, diverge about one degree in five minutes, or perhaps a very little less. He therefore drew this circle exactly 360 inches round, and marked the inches on its circumference. The pendulum was hung from the skylight immediately over the centre of the circle, the point of suspension being 25 feet high. At that length of wire, it should require 2¹⁄₂ seconds to make each oscillation across the circle. The brazen ball, which at the end of a fine wire constituted the pendulum, was furnished with a point, to enable the spectator to observe the more easily its course. A long line was drawn through the diameter of the circle, due north and south, and the pendulum started so as to swing exactly along this line; to the westward of which, at intervals of three inches at the circumference, two other lines were drawn, passing through the centre. According to the theory, the pendulum should diverge from its original line towards the west, at the rate of one inch or degree in five minutes. This, however, Mr. Jones explained, was a perfection of accuracy only attainable in a vacuum, and rarely could be approached where the pendulum had to pass through an atmosphere subject to disturbances; besides, it was difficult to avoid giving it some slight lateral bias at starting. In order to obviate this as much as possible, the steel wire was as fine as would bear the weight, ¹⁄₃₀th of an inch thick; and the point of suspension was adjusted with delicate nicety. An iron bolt was screwed into the frame-work of the skylight; into it a brass nut was inserted--the wire passed through the nut (the hollow sides of which were bell-shaped, in order to give it fair play), and at the top the wire ended in a globular piece, there being also a fine screw to keep it from slipping. * * * The pendulum was gently drawn up to one side, at the southern end of the diametrical line, and attached by a thread to something near. When it hung quite still the thread was burnt asunder, and the pendulum began to oscillate to and fro across the circle. * * * Before it had been going on quite seven minutes, it had reached nearly the third degree towards the west, whereas it _ought_ to have occupied a quarter of an hour in getting thus far from its starting line, even making no allowance for the resistance of the atmosphere.”[39]

[39] “Manchester Examiner” (Supplement), May 24, 1851.

Besides the irregularities so often observed in the time and direction of the pendulum vibrations, and which are quite sufficient to render them worthless as evidence of the Earth’s motion, the use which the Newtonian astronomers made of the general fact that the plane of oscillation is variable, was most unfair and illogical. It was proclaimed to the world as a visible proof of the Earth’s diurnal motion; but the motion was _assumed to exist_, and then employed to explain the cause of the fact which was first called a proof of the thing assumed! A greater violation of the laws of investigation was never perpetrated! The whole subject as developed and applied by the theoretical philosophers is to the fullest degree unreasonable and absurd--not a “jot or tittle” better than the reasoning contained in the following letter:--“Sir,--Allow me to call your serious and polite attention to the extraordinary phenomenon, demonstrating the rotation of the Earth, which I at this present moment experience, and you yourself or anybody else, I have not the slightest doubt, would be satisfied of, under similar circumstances. Some sceptical and obstinate individuals may doubt that the Earth’s motion is visible, but I say from personal observation its a positive fact. I don’t care about latitude or longitude, or a vibratory pendulum revolving round the sine of a tangent on a spherical surface, nor axes, nor apsides, nor anything of the sort. That is all rubbish. All I know is, I see the ceiling of this coffee-room going round. I perceive this distinctly with the naked eye--only my sight has been sharpened by a slight stimulant. I write after my sixth go of brandy-and-water, whereof witness my hand,”--“Swiggins”--_Goose and Gridiron, May 5, 1851._--“P.S. Why do two waiters come when I only call one?”[40]

[40] “Punch,” May 10, 1851.

The whole matter as handled by the astronomical theorists is fully deserving of the ridicule implied in the above quotation from _Punch_; but because great ingenuity has been shewn, and much thought and devotion manifested in connection with it, and the general public thereby greatly deceived, it is necessary that the subject should be fairly and seriously examined. What are the facts?

First.--When a pendulum, constructed according to the plan of M. Foucault, is allowed to vibrate, its plane of vibration is often variable--_not always_. The variation when it _does_ occur, is _not uniform_--is not always the same in the same place; nor always the same either in its rate or velocity, or in its direction. It cannot therefore be taken as evidence; for that which is inconstant cannot be used in favour of or against any given proposition. It therefore _is not evidence and proves nothing_!

Secondly.--If the plane of vibration _is_ observed to change, where is the connection between such change and the supposed motion of the Earth? What principle of reasoning guides the experimenter to the conclusion that it is the Earth which moves underneath the pendulum, and not the pendulum which moves over the Earth? What logical right or necessity forces one conclusion in preference to the other?

Thirdly.--Why was not the peculiar arrangement of the point of suspension of the pendulum specially considered, in regard to its possible influence upon the plane of oscillation? Was it not known, or was it overlooked, or was it, in the climax of theoretical revelry, ignored that a “ball-and-socket” joint is one which facilitates _circular_ motion more readily than any other? and that a pendulum so suspended (as was M. Foucault’s), could not, after passing over one arc of vibration, return through the same arc without there being many chances to one that its globular point of suspension would slightly turn or twist in its bed, and therefore give to the return or backward oscillation a slight change of direction? Let the _immediate cause_ of the pendulum’s liability to change its plane of vibration be traced; and it will be found not to have the slightest connection with the motion or non-motion of the surface over which it vibrates.

At a recent meeting of the French Academy of sciences, “M. Dehaut sent in a note, stating that M. Foucault (whose experiments on the pendulum effected a few years ago at the Pantheon, are of European notoriety) is not the first discoverer of the fact that the plane of oscillation of the free pendulum is invariable; but that the honour of the discovery is due to Poinsinet de Sivry, who, in 1782, stated, in a note to his translation of ‘Pliny,’ that a mariner’s compass might be constructed without a magnet, by making a pendulum and setting it in motion in a given direction; because, provided the motion were continually kept up, the pendulum would continue to oscillate in the same direction, no matter by how many points, or how often the ship might happen to change her course.”

SECTION 13.

PERSPECTIVE ON THE SEA.

It has been shown (at pages 25 to 34) that the law of perspective, as commonly taught in our Schools of Art, is fallacious and contrary to everything seen in nature. If an object be held up in the air, and gradually carried away from an observer who maintains his position, it is true that all its parts will converge to one and the same point; but if the same object be placed upon the ground and similarly moved away from a fixed observer, the same predicate is false. In the first case the _centre_ of the object is the _datum_ to which every point of the exterior converges; but in the second case the _ground_ becomes the _datum_, in and towards which every part of the object converges in succession, beginning with the lowest, or that nearest to it.

Instances:--A man with light trousers and black boots walking along a level path, will appear at a certain distance as though the boots had been removed, and the trousers brought in contact with the ground.

A young girl, with short garments terminating ten or twelve inches above the feet, will, in walking forward, appear to sink towards the Earth, the space between which and the bottom of the clothes will appear to gradually diminish, and in the distance of half-a-mile the limbs, which were first seen for ten or twelve inches, will be invisible--the bottom of the garment will seem to touch the ground.

A small dog running along will appear to gradually shorten by the legs, which, in less than half a mile, will be invisible, and the body appear to glide upon the earth.

Horses and cattle moving away from a given point will seem to have lost their hoofs, and to be walking upon the outer bones of the limbs.

Carriages similarly receding will seem to lose that portion of the rim of the wheels which touches the Earth; the axles will seem to get lower; and at the distance of a few miles, the body will appear to drag along in contact with the ground. This is very remarkable in the case of a railway carriage when moving away upon a straight and level portion of line several miles in length. These instances, which are but a few of what might be quoted, will be sufficient to prove, beyond the power of doubt or the necessity for controversy, that upon a plane or horizontal surface, the _lowest part_ of bodies receding from a given point of observation will disappear _before the higher_. This is precisely what is observed in the case of a ship at sea, when outward bound--the _lowest_ part--the hull, disappearing before the higher parts--the sails and mast head. Abstractedly, when the lowest part of a receding object thus disappears by entering the “vanishing point,” it could be seen again to any and every extent by a telescope, if the power were sufficient to magnify at the distance observed. This is to a great extent practicable upon smooth horizontal surfaces, as upon frozen lakes or canals; and upon long straight lines of railway. But the power of restoring such objects is greatly modified and diminished where the surface is undulating or otherwise moveable, as in large and level meadows, and pasture lands generally; in the vast prairies and grassy plains of America; and especially so upon the ocean, where the surface is always more or less in an undulating condition. In Holland and other level countries, persons have been seen in winter, skating upon the ice, at distances varying from ten to twenty miles. On some of the straight and “level” lines of railway which cross the prairies of America, the trains have been observed for more than twenty miles; but upon the sea the conditions are altered, and the hull of a receding vessel can only be seen for a few miles, and this will depend very greatly--the altitude of the observer being the same, upon the state of the water. When the surface is calm, the hull may be seen much farther than when it is rough and stormy; but under ordinary circumstances, when to the naked eye the hull has just become invisible, or is doubtfully visible, it may be seen again distinctly by the aid of a powerful telescope. Although abstractedly or mathematically there should be no limit to this power of restoring by a telescope a lost object upon a smooth horizontal surface, upon the sea this limit is soon observed; the water being variable in its degree of agitation, the limit of sight over its surface is equally variable, as shown by the following experiments:--In May, 1864, on several occasions when the water was unusually calm, from the landing stairs of the Victoria pier at Portsmouth, and from an elevation of 2 ft. 8 in. above the water, the greater part of the hull of the Nab Light-ship was, through a good telescope, distinctly visible; but on other experiments being made, when the water was less calm, no portion of it could be seen from the same elevation, notwithstanding that the most powerful telescopes were employed. At other times half the hull, and sometimes only the upper part of the bulwarks, were visible. If the hull had been invisible from the rotundity of the Earth, the following calculation will show that it should at all times have been 24 feet below the horizon:--The distance of the light-ship from the pier is 8 statute miles. The elevation of the observer being 32 inches above the water, would require 2 miles to be deducted as the distance of the supposed convex horizon; for the square of 2 multiplied by 8 inches (the fall in the first mile of the Earth’s curvation) equals 32 inches. This deducted from the 8 miles, will leave 6 miles as the distance from the horizon to the light ship. Hence 6² × 8 in. = 288 inches, or 24 feet. The top of the bulwarks, it was said, rose about 10 ft. above the water line; hence, deducting 10 from 24 feet, under all circumstances, even had the water been perfectly smooth and stationary, the top of the hull should have been 14 feet below the summit of the arc of water, or beneath the line of sight! This one fact is entirely fatal to the doctrine of the Earth’s rotundity. But such facts have been observed in various other places--the north-west light-ship in Liverpool Bay, and the light vessels of many other channels near the southern, eastern, and western shores of Great Britain. From the beach of Southsea Common, near Portsmouth, the observer lying down near the water, above the surface of which the eye was 2¹⁄₂ feet, and with a telescope looking across Spithead to the quarantine ship lying in the “Roads,” between Ryde and Cowes, in the Isle of Wight, a distance of 7 miles, the copper sheathing of that vessel was distinctly seen, the depth of which was about 2 feet. Making the usual calculation in accordance with the doctrine of the Earth’s convexity, it will be seen that an arc of water ought to have existed between the two points, the summit of which arc should have been 16 feet above the copper sheathing of the vessel!

From an elevation of 2¹⁄₂ feet above the water opposite the Royal Yacht Club House, in West Cowes, Isle of Wight, the pile work and promenade of the pier at Stake’s Bay, near Gosport, and nearly opposite Osborne House, were easily distinguished through various telescopes: the distance is 7 miles, the altitude of the promenade 10 feet, and the usual calculation will show that this pier ought to have been many feet below the horizon!

It is a well-known fact that the light of the Eddystone lighthouse is often plainly visible from the beach in Plymouth Sound; and sometimes, when the sea is very calm, persons can see it distinctly when sitting in ordinary rowing boats in that part of the Sound which will allow the line of sight to pass between Drake’s Island and the western end of the Breakwater. The distance is 14 statute miles. In a list of lighthouses in a work called “The Lighthouses of the World,” by A. G. Findlay, F.R.G.S., published in 1862, by Richard H. Lawrie, 53, Fleet Street, London, it is said, at page 28:--“In the Tables the height of the flame above the highest tide high water level is given, so that it is the _minimum_ range of the light; to this elevation 10 feet is added for the height of the deck of the ship above the sea. Besides the increased distance to which low water will cause the light to be seen, the effect of refraction will also sometimes increase their range.” In the “Tables” above referred to, at page 36 the Eddystone light is said to be visible 13 miles. But these 13 miles are nautical measure; and as 3 nautical miles equal 3¹⁄₂ statute miles, the distance at which the Eddystone light is visible is over 15 statute miles. Notwithstanding that the Eddystone light is actually visible at a distance of 15 statute miles, and admitted to be so both by the Admiralty authorities and by calculation according to the doctrine of rotundity, very often at the same distance, the lantern is not visible at an elevation of 4 feet from the water; showing that the law of perspective, previously referred to, is greatly influenced by the state of the surface of the water over which the line of sight is directed. A remarkable illustration of this influence is given in the _Western Daily Mercury_, published in Plymouth, of October 25, 1864. Several discussions had previously taken place at the Plymouth Athenæum and the Devonport Mechanics’ Institute, on the true figure of the Earth; subsequent to which a committee was formed for the purpose of making experiments bearing on the question at issue. The names of the gentlemen as given in the above-named journal were “Parallax” (the author of this work), “Theta” (Mr. Henry, a teacher in Her Majesty’s Dock-yard, Devonport), and Messrs. Osborne, Richards, Rickard, Mogg, Evers, and Pearce, all of Plymouth. From the report published as above stated, the following quotation is made:--Observation 6th: “_On the beach, at 5 feet from the water level, the Eddystone was entirely out of sight_.”

The matter may be summarized as follows:--At any time when the sea is calm and the weather clear, the Light of the Eddystone, which is 89 feet above the foundation on the rock, may be distinctly seen from an elevation of 5 feet above the water level; according to the Admiralty directions, it “may be seen 13 nautical (or 15 statute) miles,”[41] or one mile still farther away than the position of the observers on the above-named occasion; and yet _on that occasion_, and at a distance of only 14 statute miles, notwithstanding that it was a very fine autumn day, and a clear back ground existed, not only was the lantern, which is 89 feet high, not visible, but the _top of the vane_, which is 100 feet above the foundation was, as stated in the report, “_entirely out of sight_.”

[41] “Lighthouses of the World,” p. 36.

[Illustration: FIG. 32.]

That vessels and lighthouses are sometimes more distinctly seen than at others; and that the lower parts of such objects are sooner lost sight of when the sea is rough than when it is calm, are items in the experience of seafaring people as common as their knowledge of the changes in the weather; and prominence is only given here to the above case because it was verified by persons of different opinions upon the subject of the Earth’s form, and in the presence of several hundreds of the most learned and respectable inhabitants of Plymouth and the neighbourhood. The conclusion which such observations necessitate and force upon us is, that the law of perspective which is everywhere visible on land, is _modified_ when observed in connection with objects upon or near the sea. But _how_ modified? If the water of the ocean were frozen and at perfect rest, any object upon its surface would be seen as far as telescopic or magnifying power could be brought to bear upon it. But because this is not the case--because the water is always more or less in motion, not only of progression but of fluctuation, the swells and waves, into which the surface is broken operate to prevent the line of sight from passing parallel to the horizontal surface of the water. It has been shown at pages 16 to 20, and also at 25 to 33, that the surface of the Earth and Sea appears to rise up to the level, or altitude of the eye; and that at a certain distance the line of sight and the surface which is parallel to it appear to converge to a “vanishing point;” which point is “the horizon.” If this horizon, or vanishing point, were formed by the apparent junction of two _perfectly stationary_ parallel lines, it could be penetrated by a telescope of sufficient power to magnify at the distance; but because upon the sea the surface of the water is _not stationary_, the line of sight at the vanishing point becomes angular instead of parallel, and telescopic power is of little avail in restoring objects beyond this point. The following diagram will render this clear:--The horizontal line C D E and the line of sight A B are parallel to each other, and appear to meet at the vanishing point B. But at and about this point the line A B is intercepted by the undulating, or fluctuating surface of the water; the degree of which is variable, being sometimes very great and at others inconsiderable, and having to pass over the crest of the waves, as at H, is obliged to become A H, instead of A B, and will therefore fall upon a ship, lighthouse, or other object at the point S, or higher or lower as such objects are more or less beyond the point H.

It is worthy of note that the waves at the point H, whatever their real magnitude may be, are _magnified_ and rendered more obstructive by the very instrument--the telescope--which is employed to make the objects beyond more plainly visible: and thus the phenomenon is often very strikingly observed--that while a powerful telescope will render the sails and rigging of a ship when beyond the point H, or the optical horizon, so distinct that the very ropes are easily distinguished, not the slightest portion of the hull can be seen. The “crested waters” form a barrier to the horizontal line-of-sight, as substantial as would the summit of an intervening rock or island.