Part 5
In those parts of the building more than two storeys in height, the second horizontal tier of girders does not support a gallery, but serves only to give stiffness to the columns. The upper tier of girders, in all cases, supports the roof, which is one of the most peculiar features in the structure. In its general form the roof is flat; but it is made up of a series of ridges and furrows, the rise and fall of which is but small, and is thus arranged: the roof-girders or trusses being twenty-four feet apart, and lying in the transverse direction of the building, the space between them is spanned by light beams or rafters, which are cambered or bent upwards, and are hollowed out in a groove on the top to form a gutter. The rafters are placed eight feet apart, their ends resting on the roof-girders, and lying, therefore, in the opposite direction to them, that is, in the direction of the length of the building; these rafters are commonly called the Paxton's Gutters. Between the rafters so described, _ridges_ are supported by light sash-bars sloping up to them, at an inclination of two-and-a-half to one, and the rafter itself forms the bottom of the _furrow_. The advantage of this form of roofing is the facility it affords for the escape of the water, which runs from the surface of the roof into the Paxton's gutters; from them it is discharged into the main gutters resting on the roof-girders, by which it is conducted to the hollow columns, and passes down through them into the drains. A drop of water falling on the most distant point from the discharge would only have to traverse a distance of forty-eight feet; but in most cases the length to be passed over before reaching the down pipe would be considerably less.[5] The covering of the roof is glass, fixed between the sash-bars, which are grooved to receive it; and in order to carry off the moisture arising from condensation on the inner surface of the glass, the rafters have a small groove on each side, which makes the Paxton's gutter complete, and from which the moisture is also discharged into the main gutters. The essential portions of the roof may therefore be considered as a network of gutters; one set, the main gutters, lying in a transverse direction, and the others resting on them, and lying in the direction of the length of the building; by which arrangement any amount of surface can always be covered by roofing of a small span. The principle is precisely the same as that of subdividing large fields of arable land into strips or "lands" with furrows between them, in order to facilitate the surface-drainage.
[Illustration: VIEW OF ONE 24-FEET SQUARE BAY OF ROOF PARTLY COMPLETED.]
The outer inclosure, on the ground-floor, is formed by dividing each 24-feet bay between the columns into three 8-feet bays by half columns of wood, between which is placed boarding, held in its place by iron clips and bolts; a plinth, four feet high, is formed immediately above the floor by frames, filled with what are commonly called louvre-blades, which are hung on pivots, and of which a large number can be moved simultaneously for the admission of air; similar ventilating-frames, three feet deep, are introduced at the top of each storey round the entire circuit of the building, and by this means a ventilating-surface of no less than 40,800 square feet is obtained, or rather more than one acre.
[Illustration: PORTION OF THE LOWER STOREY OF THE PRINCIPAL ELEVATIONS.]
Externally some light arches are inserted, and open panels form the inclosure for the upper louvre-frames. The details we have been describing may be readily traced in the engraving of a portion of the lower storey as seen from the outside. The exit doors occupy one of the 8-feet bays opening about six feet wide. The inclosure to the upper storeys closely resembles those of the ground-floor, but glazed sashes are substituted for the close boarding, and the plinth is omitted. Each storey is crowned externally with a cornice and cresting ornament, and over the columns posts are carried up, to which flagstaffs will be fixed.
To return to the interior. The whole of the floor is boarded; that below is laid with an interval of half an inch between the boards, to allow the passage of dust from the millions of feet by which it will be trod; the gallery floor, on the contrary, has iron tongues between the boards to prevent the dust from coming through on the heads of the visitors below.
The roof of the transept, which we have described as crossing the building about the centre of its length, differs from that of the other parts, its general form being semicircular instead of flat, and rising above the rest of the building so as to show the whole of the semicircle externally. This roof is supported by arched timber ribs placed twenty-four feet apart, or one over every column, which forms a socket, into which the foot of the rib is fitted and secured by iron straps. Between the ribs, timbers are fixed which carry minor ribs at a distance of eight feet apart, and upon these the ridge-and-furrow roofing is constructed in the manner that has been described for the flat roofing, but following the curve of the arched ribs. At the springing or foot of the arch on either side of the transept there is a range of louvre-frames to assist in the ventilation of the building, and on the top of the arch externally a narrow passage is formed to give access to the different parts of this roof. On the inner side of the arch diagonal tie-rods are introduced between the main ribs, which, while they serve to increase the strength of the construction by tying together all the parts from end to end, produce an agreeable play of lines forming a kind of network over the whole of the surface.
The ends of the transept are closed in with fan-like tracery, reminding the spectator of the magnificent wheel windows of our Gothic cathedrals; this elegant feature is not visible in our interior view, but will be seen in some of the exteriors.
There is, perhaps, no part of this interesting building in which the great size and singular lightness, almost airiness, of the construction are so strikingly displayed as in the TRANSEPT, inclosing as it does a row of fine old elm-trees, as if to protect them in their venerable age from the smoke of the thousands of chimneys that have been gradually forming a destructive circle around them.
The only portion of solid untransparent roofing in the whole of this building is formed on either side of the arched roof just described, where there is a lead flat twenty-four feet wide. This was partly required for a platform to serve for carrying on the works for the arched roof, and was also exceedingly useful in giving access to the other roofs on either side; it likewise afforded the opportunity of giving some additional strength at the springing of the arched ribs to resist any possible tendency they might have to spread outwards.
[Illustration: View of the Interior of the Transept.]
[Illustration: View of Glass Roof from the Lead Flat.]
As the weight of such lead roofing considerably exceeds that of the glass ridge-and-furrow covering, it was necessary at the point where it crosses the wide span of the main avenue to introduce some stronger roof-girders than those used elsewhere; of these there are two on either side of the transept, the inner one of which has also to sustain two of the large arched ribs with their superincumbent roofing, and its strength is therefore increased in proportion to the additional load placed upon it. The extra-strong roof-girders are six feet deep, or twice that of the others; but their general construction is similar, the diagonal ties forming a kind of latticework, and thus keeping up the same character. These, like all the roof-girders of large span, are constructed principally of wrought-iron. Those who visited the building during its erection, and were among the fortunate few who were enabled to ascend to the "lead-flat," must have been very much struck with the singular appearance presented by the great expanse of acres of glass stretching in long lines of "ridge-and-furrow" roofing on each side of the centre, while the eye, penetrating the transparent covering, became lost in endeavouring to follow the apparently intricate lines of the interior. Such a view might fairly be said to justify the title of "Crystal Palace," by which this building is so commonly known; and it would require no great stretch of imagination to believe that it had been reared by fairy hands, as a votive offering at the world's jubilee of labour.
But we must descend again to the interior, to point out the arrangement of the offices for the staff of the Executive. The principal of these are naturally placed in the centre, on either side of the principal entrance, where they occupy in two storeys the space underneath the gallery, which is continued uninterrupted over them. The entrances at the end are also flanked by offices of less extent. The outer inclosure of these spaces is formed with glazed sashes, similar to those which are placed on the exterior of the building, and boarded partitions divide the interior. The rooms are arranged to be heated and lighted by gas when required, and ample means of ventilation are provided.
The simplicity of the construction renders it very easy to extend or contract the accommodation much more readily than would be possible under ordinary circumstances.
It now remains to notice the arrangements provided for refreshments, which are introduced in connexion with the open courts left on account of the groups of trees. These happen to occur towards the ends of the building, and on the north side of the main avenue; the space at the north end of the transept, next to the inclosed trees, is also appropriated for this purpose. The roofing over these parts is a continuation of that over the rest of the building; and the partitions necessary for inclosing the different spaces are formed chiefly with glazed sashes, avoiding as much as possible any solid construction, which would appear out of character. The open courts are inclosed with sashes and doors, rendered necessary by the uncertain nature of our climate.
A small detached building which has not been mentioned serves for the boiler-house, and is placed near the west end of the building. As it had been determined to afford the means of exhibiting some of the machinery in actual motion, it was necessary to erect boilers to supply the steam to the different machines, as it would clearly be inadmissible for each to generate steam for its own use in the building. The house to contain the boilers is ninety-six feet long and twenty-four feet wide, and is placed as near as practicable to the machinery-department; but at the same time it is quite detached from the main building to avoid risk from the fires. In appearance it resembles the one-storey portion of the main building, but it is constructed entirely of fire-proof materials. It contains five boilers, each to supply steam for twenty-horse power, which is distributed by a pipe to the different machinery.
[Illustration: General View of the Building from the South-West.]
An ornamental cast-iron railing designed by Mr. Owen Jones incloses the building, being placed at a distance of about eight feet from it along the principal fronts, but carried much further off at the ends, so as to inclose a considerable space, which will thus be available for exhibiting any large objects that will bear exposure to the weather, if there should not be sufficient room in the interior of the building. Gates are placed opposite all the entrances and exits, and these are so arranged that when closed they are uniform in appearance with the rest of the railing.
[Illustration: EXTERNAL RAILING.]
Having thus given a general sketch of the arrangement and appearance of the building, we shall proceed to describe somewhat more minutely the various details of the construction, of which the essential parts are few in number compared with the great repetition of each individually. To assist in this multiplied reproduction of the same form, some exceedingly ingenious machinery has been employed, which will therefore be described in connexion with the parts it has been used to form; and thus these will be traced through their various stages, from the raw material to their finished state as portions of the building. The greater part of this machinery has been used in shaping out those parts which are of wood, and particularly the different portions of the roof, with which we will therefore commence.
The Paxton's Gutters.
It has been mentioned that the rafters which span the space between the roof-girders serve, at the same time, as gutters, for which purpose they are hollowed out on the upper face, besides having smaller grooves at the sides to take the condensation-water. The bottom of the gutter is of a circular form, which is universally considered the best for conveying liquids with the least amount of friction, and therefore the least liable to obstruction from an accumulation of dirt.
[Illustration: SECTION OF THE PAXTON'S GUTTER, WITH THE STRONG SASH-BAR.]
[Illustration: THE CIRCULAR PLANING-MACHINE.]
[Illustration: PORTION OF PLANING-MACHINE, WITH THE REVOLVING ARM AND CUTTERS.]
A section of the gutter, as finished, is shown. To bring it into this form, after the timbers had been sawn into the requisite general dimensions they were brought under the action of the planing-machine, where they were planed on the four sides. This machine is patented by W. Furness, of Liverpool, and was worked at the Chelsea Wharf Saw-mills. The operation was effected by cutters (_a_) attached to the ends of an arm revolving with great rapidity in a horizontal plane; the timbers to be planed were wedged up into a frame (_b_) traversing on rails, and as this was passed under the revolving cutters the upper surface was removed by them, at the same time the timbers were held down upon the frame by a large iron disc (_c_) pressing upon their upper surface. The disc, together with the revolving arm carrying the cutters, was capable of being adjusted vertically to the exact dimensions of the timber. The traversing-frame was slowly propelled by the machinery, and three widths of timber were operated upon at one time. On leaving the planing-machine these quarter baulks were passed on to the gutter-cutting machine. Four different cutters were required to form the section, as shown above; they were placed one behind the other, so that the piece of timber, which was presented to their action above the centre of motion, passed over each of them in succession. The first set, which revolved in a vertical plane, roughly hollowed out the larger groove to the section shown in Fig. 1; the two next were counterparts, and formed the same section in opposite directions; they were set at an inclination to the upright of about 45 degrees, the one to the right, the other to the left; and each hollowed out one of the small side grooves, and one side of the larger gutter, leaving the section of the timber respectively of the forms shown in Figs. 2 and 3. Fig. 4 shows the form of its section after it had passed both; the fourth set of cutters again revolved vertically, and gave the gutter its finished form, as shown above. As the timber passed over the cutters it was supported at the ends on revolving rollers, and was held in its place by guiding grooves, being pressed gradually forwards against the cutters.
[Illustration: SECTIONS OF THE DIFFERENT STAGES OF THE PAXTON'S GUTTERS.]
[Illustration: THE GUTTER-CUTTING MACHINE.]
In this manner forty-two lengths of solid gutter, each twenty-four feet and a fraction long, were completed in a day of ten hours; and as the machine was worked double time, a length of more than 2,000 feet was turned out daily ready for use: this, it has been calculated, would have required the labour of about three hundred men to be employed for the same length of time. The absolute necessity for such rapid production will be evident when it is known that no less than 110,000 feet, or about twenty miles length, of such gutters were required--very nearly the distance from Buckingham Palace to Windsor Castle.
Finished as described above, the Paxton's gutters arrived at the building, where the first operation they underwent was that of cutting them to the exact length requisite. This was a nice operation, as the smallest deviation would have caused a difficulty in fitting them into their place, and to perform it a framework was constructed by which the solid gutter could be bent to the same curve it would have when fixed; a precaution that was necessary in order that the ends might be cut off quite vertically so as to fit together when in their place. At one end of this frame-work was placed a circular saw, twenty inches diameter, hung with a pulley and balance weight, so as to be moved up and down by means of a lever. The gutter being fixed in the frame by means of hinged guage-plates, one end was cut by the circular saw being brought down upon it; and at the same time another operation was performed: two cutters, placed in the centre of the circular saw, were so arranged that when brought down upon the end of the solid gutter they cut out a semi-circular notch, so that when the ends of two gutters were afterwards placed together there was a circular hole left, through which the water passed down into the main gutter. When these operations were completed at one end of the gutter, the guage-plates were taken off, and the timber was swung round on a pivot or crutch in the centre, and the same process gone through as before; the whole scarcely occupying two minutes. We shall presently have to return to this piece of machinery, as it was also used in finishing the ridge rafters.
[Illustration: MACHINE FOR FINISHING ENDS OF GUTTERS AND RIDGES.]
The solid gutter was now transferred to the hands of the carpenter, who fixed at each end, on the under-side, a small cast-iron shoe; and two struts, nine inches long, were placed so as to divide the whole length into three equal parts--the struts spread out at the top in order to present a large surface of pressure against the under-side of the gutter; and tenons projected upwards, which were fitted into mortices cut into the timber. The lower end of the struts were formed so as to give them a firm hold upon a wrought-iron rod, thirteen-sixteenths of an inch diameter, which was passed under them and through the shoes, where it was screwed up with nuts; and the struts pressing up against the timber produced the requisite bend or camber. Twenty-seven notches, to receive the sash bars, were marked with a templet and cut out on each edge of the upper-side of the gutter; and a small cast-iron plate having been fitted on the under-side at each end, the Paxton's gutter was complete and ready for fixing. The under-trussing of the rafters increased their strength considerably, so that a weight of one-and-a-half tons was required to break one which was experimented upon.
The Sash-bars.
We will next consider the sash-bars which support the ridge of the roof and receive the glass. The total length which was required of these amounts to about two hundred miles; it will, therefore, be easily understood that mechanical contrivance for cutting them out became an absolute necessity; this Mr. Paxton appears to have discovered in his works at Chatsworth, as he mentions in his lecture.
[Illustration: MACHINE FOR CUTTING OUT SASH-BARS.]
The sash-bars are one inch thick and one-and-a-half inches deep, and are grooved on each side, besides having all the four edges bevelled or chamfered; all which was done in one passage through the machine. The plank which was to form the sash-bars was passed in at one end of the machine, between pressure-rollers; it then passed between cutters placed both above and below it, which made about twelve hundred revolutions per minute, and hollowed out the different grooves; and, lastly, it passed between circular saws which divided it into separate sash-bars, after which they had only to be cut into their proper lengths.[6] The exact length of each sash-bar when finished is four feet one inch.
In this state the skylight bars were sent to the building, where they underwent several finishing operations, necessary to make the ends fit down into the notches prepared in the ridges and gutters. Thirty of the bars were first placed together in a horizontal traversing-frame on a saw-table, on each side of which circular saws were fixed at the distance of the required length of the sash-bar; the frame was then moved forward against the saws, so that both ends of the whole set of bars were cut off simultaneously, and at the same time a cut was made at one end half-way through the bar, in order to form the shoulder against the gutter. They were then removed to another bench, where the end of the bar was bevelled and the shoulder formed by means of a small instrument having a handle with two projecting jaws fitting into the ends of the glass grooves of the bars; between these there was a small blade which, being pressed down, cut out the shoulder which had been sawn through in the other direction, and another blade was placed at the proper angle to remove the bevelled piece at the end of the bar.
[Illustration: THE SASH-BAR DRILLING-MACHINE.]
One more process made the sash-bars complete for fixing--this was the drilling a hole at each end to nail them down on the gutter and ridge; and this was also done by machinery, to insure all the holes being drilled at the same angle. On one side of a horizontal bench were placed a set of four-inch driving pulleys (_a a_), with as many horizontal drills projecting towards the other side of the bench; a wooden traversing-plate (_c_) opposite each drill, and working towards it, received one end of the sash-bar, while the other rested in an inclined position against a wooden rail (_b_) placed longitudinally above the pulleys, having as many sinkings thereon as there were drills. The traversing-plate being then pushed forward, the sash-bar was perforated by the drill; the plate was then drawn back, and the same operation repeated with the other end of the bar, which left it ready for fixing.
The action of the traversing-plate (_c_) is shown more distinctly in the second engraving.[7] One out of every nine of the sash-bars of the roof is stronger than the rest, to serve for fixing the ridge previous to glazing. These extra-strong bars are two inches wide and one inch and a half deep, and were formed by the same machinery already described, by an adjustment of the different cutters and saws.
[Illustration: PORTION OF SASH-BAR DRILLING-MACHINE.]
The Ridges.