Roof of Transept.
WE will now return to describe that portion of the roof which varies in form and arrangement from the rest, namely, the semicircular covering of the transept. This is supported by arched ribs, placed twenty-four feet apart, and constructed of Memel timber, in three thicknesses; the centre-piece four inches thick, with a 2-inch piece on each side of it. They are formed in lengths of about nine feet, placed so as to break joint; that is, the joints of the outer pieces fall upon the centre of the inner one. The thicknesses are fastened together by bolts passing through them about two feet six inches apart, besides being nailed at other points. On the inner circumference of the rib thus constructed there is then placed a piece of timber moulded to correspond with the form of the columns; and on the outer circumference two boards, each one inch thick, are bent round and attached to the rib with strong nails. On both the outer and inner circumference a flat bar of iron is secured by bolts passing through the whole depth of the rib, which, thus finished, measures eighteen inches in depth by eight inches in thickness. The ends of the ribs are fitted into sockets, formed by the upward continuation of the columns, to which they are attached by iron straps.
The ribs, which are supported by the trusses over the main avenue, have their ends bolted down upon a piece of timber secured on the upper portion of the truss; and they are further fixed in their places by oak brackets, forming a spreading foot on each side upon the same piece of timber.
Between these large ribs horizontal timbers, called "purlins," are fixed about nine feet apart, by means of cast-iron shoes, bolted both to them and to the ribs. These serve to support the minor or intermediate ribs, occurring at distances of eight feet apart; which consist of a single square piece of timber, having the two thicknesses of 1-inch board bent round their outer circumference, as on the main ribs. The boards form the gutters or furrows between which rise the ridges, in the same manner as in that portion of the roof which is horizontal.
The ridges, in this case, instead of being cut out of solid pieces, are formed in three thicknesses, bent round to the requisite curve, and so retained by small bolts tying them down to the "purlins." The sash-bars which receive the glass form, as elsewhere, the sloping rafters or supports of the ridge.
Interior View of the Central Avenue towards the West.Interior View of the Central Avenue towards the West.
Interior View of the Central Avenue towards the West.
Interior View of the Central Avenue towards the West.
The space below the first "purlin" or plate at the springing of the arch, down to the level of the lead-flat beneath it, is fitted with louvre-frames for ventilation. The diagonal bracing between the main ribs has been already alluded to. Each set consists of four wrought-iron rods three quarters of an inch in diameter, having eyes at one end, by means of which they are secured with bolts, passing through the thickness of the ribs; in the centre they meet in a cast-iron ring, on the inner side of which the ends are screwed up with nuts.
The semicircular ends of the transept are filled in with tracery, formed by radiating timbers, strutted apart with short pieces placed in concentric rings. The circular heads of the openings are formed by iron castings screwed into their places, and the eye from which the radiating lines of the tracery proceed is also formed by solid iron castings bolted together. On the outer face the ribs of the tracery are moulded, and on the inner side glazed sashes are fixed, filling in the openings.
The lead-flat, twenty-four feet wide, extending the whole length of the transept, on either side of the semicircular roof, is constructed in a similar manner to the floor of the galleries, by under-trussing two pairs of joists in each bay. In the width of the lead-flat roof a horizontal truss is formed by flat bars of iron fixed in the direction of the diagonal of the 24-feet square bays, to resist any possible thrust or tendency of the ends of the ribs to open outwards at the springing.
The Facework.
THE external inclosures of the building, on the levels of the different storeys, require but little description in detail beyond that already given. The sash-bars dividing the sashes of the upper tiers are grooved for glass similarly to those used in the roof, and were cut out by the same machinery. The glass was put in after they were framed together, so that it was necessary to arrange the ends of the bars that it could be slipped in at one end. As the bars of these sashes were of slight dimensions and considerable length, they were strengthened by wrought-iron rods passed through the sash-frame and the bars, and screwed up at the ends, causing the whole to work together. The sashes are held in their position by small cast-iron clips, which are bolted on to the columns; and as the surface presented to the wind by the upright sides of the building is of such considerable extent, wooden bridges are fixed against the sashes on the inside, by small cast-iron shoes bolted to the columns; and at the internal angles, where the wind would exert its greatest force, these bridges are further strengthened by wrought-iron rods half an inch in diameter, pressing against the back of them, which is grooved for the purpose, and screwed up at each end in the cast-iron shoes. In this manner a connected chain of resistance to any external pressure is established round the whole circuit of the building.
THE LOUVRE-FRAME.THE LOUVRE-FRAME.
THE LOUVRE-FRAME.
THE LOUVRE-FRAME.
The louvre-frames, which form part of the face-work in all the different storeys, consist of a deal frame in which bent louvre-blades are hung on pivots at each end. These blades are of galvanised iron of anS sectionform. On the back of each blade is fixed a loop of thin iron, to which a rack is fitted; and by these means all the blades in each frame are moved simultaneously. A considerable number of these racks may also be connected, so that a large area of ventilation may be regulated at once.
The Diagonal Bracing.
FROM the total absence in this building of any internal division-walls, which in ordinary structures considerably add to their stability, it was thought desirable to introduce into the construction something to compensate for this deficiency. At several points in the length of the building, where a continuous connexion could be established transversely, the squares formed by the columns and girders on the different storeys have their four corners connected by diagonal rods, seven-eighths of an inch in diameter, having eyes at the ends, by which they are secured to the bolts connecting the different parts of the columns. In the centre of the square the four rods meet in a cast-iron ring, and are screwed up with nuts; ornamental faces are fitted into the rings, so that this addition to the construction is by no means detrimental to the general effect.
In a similar manner this diagonal bracing is introduced in a horizontal direction immediately under the floor of some portions of the galleries; of these there are twenty-two sets, and of those placed vertically there are, altogether, 220 sets in the building, and the manner of their introduction will be readily understood from the views of the interior.
The Staircases.
THE double staircases, of which it has been mentioned there are eight in the building, consist each of four flights, about eight feet wide; two parallel ones, leading from the ground-floor to a landing, at the half-height, and the other two branching in opposite directions from the landing to the two galleries. The treads of the steps aremade of a species of mahogany called sabicu, which is much harder than oak, and therefore peculiarly suited to the purpose for which it is here employed. The risers, or faces of the steps, are of deal. The stairs are supported by cast-iron girders, following the slope, the lower ones being fixed at the foot to stout timbers under the flooring, and the upper ends bolted to the cast-iron columns which support the landing. These columns are of the same pattern as the rest throughout the building, but only five inches in diameter. They are supported on concrete, and eight of them are required for each staircase. The floor of the landing is carried by lesser cast-iron girders, with flooring-joists.
VIEW OF STAIRCASE.VIEW OF STAIRCASE.
VIEW OF STAIRCASE.
VIEW OF STAIRCASE.
The girders carrying the upper flights spring from the landing girders, and have their upper ends bolted on to the main girders supporting the galleries, which are varied in pattern for this purpose. The railing of the staircase is formed in separate cast-iron standards, one to each step, which are bolted on to the top flange of the girders; and the foot of the standard is so continued that the ends of the treads are fitted into it, and are thus supported. The pattern of these standards is assimilated to that of the gallery railing.
The hand-rail is formed of Honduras mahogany, with carved ends. On each side of the upper flight, which occupies the centre of a 24-feet space, connecting-galleries about eight feet wide are carried, establishing a communication between the two lines of gallery without descending to the level of the landing and then re-ascending. The landing is sufficiently high above the ground-floor to give ample headway for passing underneath it; so that the space occupied by the staircases on the ground-floor is but small.
The Floor and Foundations.
IT now only remains to mention briefly the construction of the floor of the building, and the foundations for the base-pieces. The substratum of the site consists of gravel of an excellent quality, and sufficiently dense to have sustained, perhaps without any preparation, the load brought upon it by the bases of the columns. A thickness of concrete, proportioned in all cases to the amount of the weight to be borne by the superincumbent columns, and of such a size as to be two feet in each direction larger than the bed-plates, was placed upon the gravel, and the upper surface was finished with a bed of fine mortar to receive the bed-plates. In this manner it was calculated that in no case would a greater weight than two-and-a-half tons be borne by each foot superficial of the gravel—previous experiments having shown that a considerably larger weight could be placed upon it without any injurious effect.
The timbers supporting the joists for the floor are also placed upon small blocks of concrete, about one foot cube, at a distance of eight feet apart. On these are fixed the flooring-joists, and a deal floor an inch and a half thick is laid on them, as has been already mentioned, with intervals of about half an inch between the boards.
FIXING CAST-IRON DRAIN-PIPE.FIXING CAST-IRON DRAIN-PIPE.
FIXING CAST-IRON DRAIN-PIPE.
FIXING CAST-IRON DRAIN-PIPE.
In order to carry off the water brought down from the roof by every alternate longitudinal row of columns, 6-inch cast-iron pipes are fitted into the sockets described in the base-pieces, and are carried in the lines of those columns through the whole length of the building, with discharges into thelarger drains at the centre and at each end; the natural slope of the ground gives a sufficient fall to the pipes.
Having thus described in detail all the different portions of the construction of the building, we must proceed to give some account of its actual erection, which will enable us to mention many very ingenious mechanical contrivances which were employed in the course of its progress.
The First Operations on the Ground.
FROM the great extent of the area required for the building, it was not to be expected that any site would be found of the necessary size, perfectly level. On the ground occupied by the building there is a difference of level between the two extreme ends of about eight feet. In consequence of this fall of the natural surface from west to east, and in order to avoid having a considerable flight of steps at one end of the building to compensate for it, it was determined to arrange the floor with an inclination following nearly that of the ground, such fall being at the rate of one inch in twenty-four feet. All the lines of the building which would be called horizontal in fact follow this line of the floor, and those which are supposed to be upright are placed at right angles to the floor, and therefore slightly inclined from the perpendicular towards the east. The deviation, however, is so exceedingly small as to be perfectly imperceptible even to those who are aware of the fact; and no one who was not previously informed of it would be able to detect it.
It has been mentioned that Messrs. Fox and Henderson's tender for the building was verbally accepted on the 16th of July, 1850, and on the 30th of that month they obtained possession of the site from the Commissioners of Woods and Forests.
The first proceeding was to inclose the whole area (including a considerable space at each end more than would be covered by the building) with a hoarding about eight feet high, put together in a very simple manner, so that the boards were afterwards available for the flooring. The supports for the hoarding consisted of pieces of timber fixed in the ground in pairs, at intervals of the length of the boards, leaving a narrow space between them, into which the boards were dropped, and thus held in their place without any nails. Temporary offices were then erected in a convenient portion of the site, and were covered with a roofing which was a specimen of that to be used in the building itself. Considerable ranges of carpenters' sheds were also put up, and even stables for twenty or thirty horses, which were required in the progress of the works.
Setting out the Ground.
THE first thing to be done towards the building itself was to set out accurately all the points where the columns would stand, as well as the general outline of the building. It will be readily understood that this was an exceedingly important part of the work, as upon its accuracy depended the fitting together of the various parts that had afterwards to be put in place.
This part of the work was executed with great precision by Mr. W. G. Brounger. He commenced by determining the four extreme angles of the building, and the centre lines of the main avenues. These formed fixed points from which were determined the whole of the centres for the columns.
Our readers will recollect that the dimension of twenty-four feet occurs horizontally throughout the building, either in multiples or sub-multiples. In order to measure off the different distances, rods of American pine were made, into which, near the ends, pieces of metal were fixed, having corresponding notches at the exact distance of twenty-four feet apart. By these means the lengths were measured off with great accuracy, as the wood used is not liable to alteration in the length of its fibre; and by means of the metal notches the rods were sure to be placed correctly together. It was necessary to make these sockets or notches of metal, from the great amount of work the rods had to perform.
In determining the length of the rods, the standard of the Astronomical Society was used; and this was referred to in all important measurements for the castings and other parts of the building, to insure their precise eventual agreement in length. This will hardly be considered to have been unnecessary when it is remembered that, from the great length of the building, a very minute error in any of the parts would have been so multiplied as sensibly to throw out the ends.
To those who are unacquainted with the fact, it may be well to mention that the standard of length referred to is obtained from a pendulum, which oscillates seconds, in the latitude of London, in a vacuum, at the level of the sea, at a certain fixed temperature. The length of this pendulum is then divided into a certain registered number of feet and inches.
The rods above described were carried along the centre lines of the columns, and the position of each column was marked by a small stake driven into the ground; and in order still more accurately to fix the centre, a long nail was driven into the head of the stake. In this manner the position of every column throughout the building was determined.
The level at which the floor was to be fixed was the next pointdetermined by the ordinary method of levelling, and stakes, with aT sectionpiece at the top, called boning-sticks, were fixed in different parts of the building; by the aid of which the tops of the base-pieces for the columns were all afterwards fixed in one plane of the required slope.
Fixing the Base Plates.
THE next proceeding was to excavate the holes for the concrete, on which the base-pieces were to stand. To do this, the stakes marking the centres of the columns had to be removed, and it was therefore necessary to adopt some method of finding those centres again with precision. For this purpose a large carpenter's square, as it is called, was made. This instrument forms a right-angled triangle, and in this instance was used in the following manner:—The centre of its longest side, or hypothenuse, was marked by a line, which, if continued, would pass through the right angle of the triangle, and at an equal distance along each of the other sides of the triangle from the right angle an upright saw-cut or notch was made. The square was then placed horizontally, so that the line marked on the hypothenuse coincided with that of the centres of a row of columns, and so that the right-angled corner of the square touched the nail marking the exact site of a column. Two small stakes were then driven under the notches in the short arms of the square, and nails were driven into them through the notches. It will be seen that by these means the site of the first stake could easily be again ascertained after its removal. The holes for the concrete were then dug of an oval form and of the various sizes and depths required, and the concrete filled in to the proper height. The gravel used for the concrete was raised in a pit at one end of the ground.
Next to the setting out of the positions of the columns, perhaps the operation of fixing the base-pieces was that in which the greatest accuracy was required; for as there were in some parts three storeys of columns to be fixed over them, any inaccuracy as to their level or position would be very much increased at the top of the building. To fix the base-pieces over the centres that had been determined for the columns, another carpenter's square was made use of, like that already described, but having the right-angled corner cut out to the form of the section of a column. This square being placed with the notches in its short sides over the two stakes already described, the upright portion of the base-piece was fitted into the notch at the angle; and as the reader will at once see, if he has followed us in the description of the various processes, its correct position was thus exactly found.
In order to determine the level of the top of the base-pieces, boning-sticks were placed in the lines of the columns, and when the base-piecehad been approximately fixed, a piece of wood was placed on it edgeways, the top of which was to range with the top of the boning-sticks. This was easily arranged by looking along them; and the workmen drove down the base-piece with a wooden mallet till the desired level was obtained.
From what has been previously stated, it may be gathered that the base-pieces had to be fixed truly upright in one direction, but slightly inclined in the other; and to effect this a plumb-rule was made, on which the deviation from the perpendicular line was marked; and this, when applied to those faces of the base-pieces which were to incline, served to show when the proper inclination was arrived at, whilst an ordinary plumb-rule applied to the other upright faces tested their vertical position.
The first column was raised on the ground on the 26th of September, but little more than two months after the tender had been accepted. In the meantime, many of the different castings had already arrived on the ground, and a considerable advance had been made in the carpenter's work for the gutters and other parts. The semi-circular ribs for the transept roof were also being put together, and stacked in such a manner as not to stand in the way of the other works.
VIEW OF CRANE AND PROVING-PRESS.VIEW OF CRANE AND PROVING-PRESS.
VIEW OF CRANE AND PROVING-PRESS.
VIEW OF CRANE AND PROVING-PRESS.
We may mention here that every casting, as it came on to the ground, was weighed and registered, and every girder proved, as already described; in doing which considerable assistance was derived from one of Mr. Henderson's patent Derrick cranes, which was erected near the proving-apparatus. By its means a girder was raised from the waggon in which it arrived, placed on the weighing-machine, weighed, removed to the proving-press, tested, raised again, and deposited on the ground in a stack, in less than four minutes.
Henderson's Derrick Crane.
ABRIEF description of this useful engine may not be out of place here. It consists of an upright mast (E), steadied when the crane is in use by two sloping stays (F F). These stays are fixed into horizontal timbers (G) on the ground, connected with the foundation-plate (H) on which the mast turns. At the foot of the mast is fixed a combination of wheels and working handles for raising the weight, technically called a crab. A beam (A) working at the bottom in a socket (B, Fig. 3) fixed to the foot of the mast, but hanging out from it in a sloping direction, is called theDERRICK, and forms the principal peculiarity of the crane, as it can be raised more to the upright line, or lowered to slope more outwards, as may be desired, by means of the chain (C). The advantage of this is obvious; for a weight may thus be raised from or deposited at any point within a circle of a certain radius, depending on the length of the derrick; whereas, in an ordinary crane, the weight can only be placed at points upon the circumference of that circle. The whole engine revolves on a pivot (H, Fig. 2) at thefoot of the mast. Cranes of this description are made varying in power from one to forty tons, and with derricks ranging from twenty to sixty feet radius.
Raising and Fixing the Columns and Girders.
MANY of the persons who visited the building during the progress of its erection were heard to inquire "where was the scaffolding;" and others even imagined that the skeleton framework they saw was, in fact, only the scaffolding for the building, and not parts of its actual construction. This leads us to point out one of the most interesting peculiarities of the structure; namely, that it formed, as it were, the scaffolding for its own erection. In order to raise the columns upon the base-pieces, two poles were placed upright, connected by a horizontal piece, forming what is called shear-legs; the whole being steadied in its position by ropes from the summit fixed to the ground in various directions. A rope with pulleys fixed to the horizontal piece served to hoist the column, and sustain it in a vertical position until the bolts were passed through the projecting rings at the bottom of the column and the corresponding ones at the top of the base-piece, and screwed up. When two columns had been thus fixed, a connecting-piece was attached to each end of a girder, and the whole raised by the same apparatus, and fixed on the top of the columns; bolts being passed through the holes in the projections of the connecting-pieces, corresponding with those on the top of the columns. The shear-legs were then moved on twenty-four feet to perform the same duties to another pair of columns; and two sides of a 24-feet bay were thus formed. To complete the square, two more girders were raised in a similar manner, and fixed between the connecting-pieces over the columns. The square bay then became a firm structure, requiring no further support; and by repeating these operations all the smaller avenues of the building were erected, of the different heights of one, two, or three storeys. The greatest number of columns thus fixed in one week was 310.
FIXING THE GIRDERS.FIXING THE GIRDERS.
FIXING THE GIRDERS.
FIXING THE GIRDERS.
General View of the Works in Progress.General View of the Works in Progress.
General View of the Works in Progress.
General View of the Works in Progress.
Hoisting the Roof Trusses.
THE wrought-iron roof-trusses over the 48-feet avenues were raised in a similar manner to the columns and girders; and in all cases horses were employed to run out the end of the fall-rope, which was passed through a pulley or catch-block at the foot of the shear-legs, in order to change its direction from vertical to horizontal.
For raising the roof-trusses of seventy-two feet span over the main avenue a somewhat different method was employed. A single mast or derrick, more than seventy feet high, was placed in the centre of the avenue, and steadied in an upright position by guide-ropes spreading from the top in various directions. Near its summit the hoisting-tackle was firmly lashed on. The trusses to be hoisted were brought from the places where they had been put together, and placed across the main avenue at the points where they were to be fixed. Two ends of a stout chain were passed round the upper portion of the truss, at points dividing its length into about three equal parts. To this chain the hoisting-tackle was attached, guide-ropes being further fastened to each end of the truss to steady it in its ascent. In order to stiffen the truss horizontally, struts were attached at the centre projecting on each side, and held in their place by tie-rods attached to the upper part of the truss, and forming a triangle on each side. Before the truss, therefore, could bend in a horizontal direction, the attachment of these tie-rods must have given way. Six horses drew out the end of the fall-rope, and in the course of a very few minutes the truss was hoisted to its giddy height, and each end slipped in between the projections made in the connecting-pieces to receive it.
The animated scene presented by these operations was highly interesting from the number of men employed, both on the ground and for fixing the trusses in their position aloft, and from the rapid progress so many hands made. Each gang of men was managed by a foreman, who was obliged to issue his orders through a speaking-trumpet, to enable his voice to be heard in the din caused by the other works going on around. Besides the two large gangs of men engaged in the hoisting of the trusses, other smaller gangs were at work at different points getting up the columns and girders. In one part, the roofing of which was completed as early as practicable, a crowd of carpenters were preparing the Paxton's gutters and other portions of the work. In another place, as soon as a sufficient space could be roofed over and a temporary floor laid, various parts of the machinery we have already described were fitted up and worked by portable steam-engines. Of these there were three in different parts: one drove the machinery for finishing the sash-bars, gutters, ridges, &c.; another worked the drilling, punching, and other machinery connected with the iron-work; and a third was used for working circular saws.
Of the number of trusses that were hoisted as above described, in only one instance (and that the first) was the result otherwise than perfectly successful. The first truss was raised by its ends, instead of from the centre; but that method was afterwards abandoned, from the difficulty of maintaining the truss in an upright position during its ascent; which was important, as, if it turned on its side, its lateral strength was not sufficient to prevent it from bending, which would have destroyed the joints of the work.
One of the tall masts was worked on each side of the transept, from the centre to the ends of the building, being maintained constantly in an upright position, while traversing from point to point, by alternate slackening and hauling up of the ropes which steadied it; and it was curious to witness the motion of these tall giants, as they slowly progressed from one point to another, in the performance of their important office. Stout planks were laid along the ground, upon which the foot of the mast was forced forward by crowbars and levers; the planks served also to distribute the weight, which would otherwise have sunk the end into the ground. As many as seven trusses were hoisted in one day by each derrick, which had therefore to travel a distance of 168 feet.
So careful were the men, under the direction of the manager (to whom was intrusted the active superintendence of the whole erection of the building), that no accident of importance occurred in these difficult operations.
HOISTING THE 72-FEET TRUSSES.HOISTING THE 72-FEET TRUSSES.
HOISTING THE 72-FEET TRUSSES.
HOISTING THE 72-FEET TRUSSES.
Provision for Expansion of Girders.
IN connexion with the fixing of the girders, it may be desirable to mention the provision that was made for the expansion and contraction of the iron, which in so great a length as that of the building might have otherwise produced results prejudicial to its stability.
Between the projections cast on to the connecting-pieces and those projecting from the ends of the girders which they were made to clip, sufficient space was left for the introduction of oak keys, by driving in which the girder was fixed in its place, whilst the compressibility of the wood left sufficient play for the expansion of the metal. In describing the girders, it was mentioned that in the upper and lower flat flanges small sinkings were cast near the ends. Corresponding with these sinkings, a notch was left in the projection which came out from the connecting-piece; and when the girder was put into its place, iron wedges were driven in between the notch and the sinking, by which means any lateral motion of the girder was prevented. It was a great advantage to have the means of fixing the girders of so simple a nature, as any arrangement presenting the least complication, or requiring great nicety, would have materially retarded the progress of the work.
The wrought-iron trusses were held by the connecting-pieces in a similar manner to the cast-iron girders; but, as an additional security, bolts were passed through holes provided in the standards at the ends, and through the connecting-pieces, where they were screwed up with nuts.
The raising and fixing of the extra-strong roof-trusses crossing the main avenue near the side of the transept required particular care, from their great weight; the heaviest being, as we have before mentioned, no less than eight tons. These trusses were the first that were fixed across the central avenue, and about 150 men were engaged in the hoisting of each one. They are secured to the columns by four strong bolts passing through the end-standards.
In order to provide additional support for the great weight brought upon the last-mentioned trusses by the transept roof, extra columns were introduced underneath them. These were built up in storeys corresponding with those of the other columns, with which they were connected, at the levels of the girders, by bolts and straps. A cast-iron shoe, fixed on the top of the columns, provided a bearing for the ends of the truss. The columns just described project slightly into the main avenue from the line of the other columns; and this is the only instance in the interior of the building of the iron columns occurring at a less distance than twenty-four feet apart.
Glazing the Roof.
WE have now traced the erection of the building up to the level of the roof, in which it will be readily conceived the operation of glazing was one of extreme difficulty, there being no scaffolding to aid the workmen in conducting their operations. When the glazing was first commenced a light scaffolding was suspended from the rafters; butthis was found to be too tedious and troublesome a method of proceeding for so large an extent of roofing. It was, moreover, of great importance that some means should be devised for completing this part of the construction independently of the weather; a matter of some moment, when it is remembered that the work had to be done in the winter, when in our climate such operations are liable to be very much impeded by heavy rain. The arrangements made to meet this difficulty, as well as some others for carrying on the works, are very clearly described in a paper by Mr. Digby Wyatt, read at the Institution of Civil Engineers, on the 14th January, 1851, from which we quote some passages, by permission, for the benefit of our readers.
With reference to the means employed for glazing the roof he says: "To effect this purpose, a travelling stage was devised by Mr. Fox, which superseded the necessity of any scaffolding for glazing, and by means of seventy-six of these machines nearly the whole of the work has been executed. The stage was about eight feet square, and rested on four small wheels travelling in the Paxton's gutters. It thus embraced a width of one bay of eight feet of the roof, with one ridge and two sloping sides. Each bay in width required, therefore, a separate stage."
"Each stage was occupied by two workmen, and was covered by an awning of canvass stretched over hoops, to protect them in bad weather, and was further provided with a box on each side to contain a supply of glass. The sash-bars and other materials were piled upon the stage itself, the centre of the platform being left open for the convenience of hoisting up materials, for which purpose there was a small iron arm with a single block pulley."
GLAZING-WAGGON, FOR FLAT ROOF.GLAZING-WAGGON, FOR FLAT ROOF.
GLAZING-WAGGON, FOR FLAT ROOF.
GLAZING-WAGGON, FOR FLAT ROOF.
"Whilst working, the men sat at one end of the platform (the ridge having been previously fixed in position by means of the extra-strong sash-bars), and they fixed the glass in front of them, pushing the stage backwards as they completed each pane. On coming to the strong sash-bars previously fixed, they temporarily removed them to allow the stage to pass. In this manner each stage travelled, uninterruptedly, from the transept to the east and west ends of the building, and the glaziers were enabled to follow up the previously-fixed work very closely. The average amount of glazing done by one man per day was fifty-eight squares, or about 200 superficial feet; and the largest amount done by any one man in a working-day was 108 squares, or 367 superficial feet."
The mode of fixing the squares of glass was this: a sash-bar having been nailed down between the ridge and the gutter, the workman inserted one long edge of a square of glass into the groove in the sash-bar, he then placed a loose bar against the other long edge of the glass and brought the whole down to bear upon the ridge and gutter, the second sash-bar fitting into the notches prepared for it; the glass was then pressed up a little, in order to insert its upper edge into the groove in the ridge, and the workman then filled in the grooves on the outside of the glass with putty, the lower edge of the glass having been also bedded on putty where it bears on the edge of the gutter. The ends of each sash-bar were fixed with a nail driven into the holes previously drilled.
Stage for Repairing Glass.
AS it might naturally be expected that out of the thousands of panes of glass employed, particularly in the flat roof of the building, many would be broken in the course of the works, subsequently to their being fixed, it was necessary that a ready means should be devised for repairing any such damage, as the glazing-waggons used for the first execution of the work would not be available for that purpose. A light stage was therefore constructed, travelling with wooden wheels upon the ridges instead of in the gutters; and from this the men were able to perform their work without walking along the narrow gutters, which would have been attended with much risk. This stage was also used for fixing the canvass on the outside of the roofing, where it is nailed along the ridges, and allowed to bag down slightly between them. The object of the canvass, which covers externally the whole of the roof except the transept, is twofold: it preserves the glass from damage, and also protects the objects exhibited from the direct rays of the sun, which would, of course, in many instances, be very prejudicial; for the latter purpose the upright sashes on the south side are also covered with canvass on the inside.
Hoisting the Ribs for Transept Roof.
ONE of the most interesting operations which attracted the attention of the numerous visitors to the works was the raising the ribs for the semicircular roof of the transept, the description of which we give from Mr. Wyatt's paper:—
"The operation about which most anxiety had been felt was the hoistingof the arched ribs of the transept. These ribs were constructed on the ground horizontally, and when completed with all their bolts, two of them were reared on end, and maintained in a vertical position, at a distance of twenty-four feet from each other, by guy-ropes. As the ribs singly possessed little lateral stiffness, they were framed together in pairs with the purlins, intermediate small ribs and diagonal tie-rods, forming a complete bay of the roof twenty-four feet long; two complete sets of temporary ties were also introduced to provide for the strains incident to the variations in position of the ribs during the hoisting. The feet of the ribs were bolted on to a stout piece of timber, and the lower purlins strutted up from the same." In this state the framework is shown in the engraving.
A PAIR OF RIBS PREPARED FOR RAISING.A PAIR OF RIBS PREPARED FOR RAISING.
A PAIR OF RIBS PREPARED FOR RAISING.
A PAIR OF RIBS PREPARED FOR RAISING.
"The whole framework was then moved on rollers to the centre of the square formed by the intersection of the transept and the main avenue, where it was afterwards hoisted. All the ribs were landed over this square, and were afterwards moved on a tramway formed of a half baulk of timber constructed over the columns on either side of the transept, at a height of about four feet above the lead-flat. The hoisting-tackle consisted of four crabs, each one being placed on the side of the transept opposite to the part of the ribs to be lifted by it, so that the men at the crabs might watch the effect of their exertions with greater convenience."
"The hoisting-shears were placed on the lead-flat immediately over the deep trusses of seventy-two feet span; each set consisted of three stout scaffold-poles, lashed together at the top, and footed on planks laid across the flat, and secured by the necessary guy-ropes. The hoisting-rope passed from each of the crabs across the transept horizontally, to a leading block attached to the foot of the opposite angle column of the square; it then passed up to a treble block fastened to the shears on the flat, and from thence down to a double block secured by chains to the bottom part of the ribs."