SECTION VI.-THE CONSTRUCTION OF THE BUILDING.

ON the 30th July, 1850, the contractors obtained possession of the site from the Commissioners of Woods and Forests.

The first proceeding was to enclose the whole area, together with an additional space at each end, with a hoarding about 8 feet high. The boards used for the purpose were afterwards employed for the flooring of the building, and to prevent their being disfigured by nails, they were supported by pieces of timber, afterwards used as joists, 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. Temporary offices were erected, as also carpenters' shops, and stables for 20 or 30 horses employed upon the works. The general outline of the building, and all the points where columns would stand were then accurately set out. This was done by determining the 4 extreme angles of the building and the centre lines of the main avenues, which formed fixed points from which were determined the whole of the centres for the columns. The unit of horizontal measurement, viz. 24 feet, which occurs throughout the building, either in multiples or submultiples, was secured by measuring rods made of well-seasoned American pine, into which, within a few inches of each end, were fitted gun-metal cheeks or small projecting plates, the inner edges of which were set at exactly 24 feet apart; so that by laying one pole upon another, the inner edges of the cheeks of two separate poles were brought into contact. The length of the rods was determined by the Astronomical Society's Standard, which was referred to in the measurements for the castings, and other parts of the building. This precaution was necessary, since from the vast extent of the structure, a small error in any of the parts would have been so much multiplied as to become sensible at the ends. The measuring rods 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 the centre was accurately fixed by a long nail driven into the head of the stake. The level for the floor was determined by the ordinary method of levelling; and stakes, with a T piece 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 afterwards fixed in one plane of the required slope.

The base plates for the columns were fixed on concrete, contained in holes excavated for the purpose. But in making these holes the stakes which marked the centres of the columns had to be removed, and in order to find those centres again, a large, wooden, right-angled triangle, or carpenter's square, was used in the following manner :-at the two ends of the right-angled triangle saw-cuts were made, and before the removal of the stake, the apex of the triangle was set to the nail which indicated the situation of the centre of the column: two other stakes were then driven into the ground beneath the saw-cuts, and two nails were driven in at the ends of the saw-cuts. The wooden triangle being next removed, the centre stake was withdrawn, the hole excavated, and the concrete thrown in. The height of the surface of the mortar, varying, as it did, with almost every column, on account of the ground not being level, was regulated by pegs driven in to the correct level. In order to fix the base-plates over the centres determined for the columns, another carpenter's square was used, the right-angled corner of which was cut out to the form of the section of the upright portion of the base-piece, which was the same as that of a column. This square being placed with the notches in its short sides over the two stakes already noticed, the upright portion of the base-piece was fitted into the notch. at the angle, and thus its correct position was found. 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-piece had been approximately fixed, a piece of wood was placed on it edgeways, the top of which was made to range with the top of the boning sticks; the base-piece being driven down with a wooden mallet until the desired level was obtained. Each base-piece was fixed truly upright in one direction, and slightly inclined in the other by means of plumb rules, on one of which the deviation from the perpendicular line was marked, and this being applied to those faces of the base-pieces which were to incline, served to show when the proper inclination had been attained,

while the other plumb rule, applied to the upright faces, showed when they were truly vertical. Great care was required in fixing the base-pieces; for as three stories of columns were in some places to be fixed over them, any inaccuracy in their level or position would be very much increased at the top of the building.

The base-plate is shown in Fig. IX. The lower part consists of a horizontal plate, attached to which is a vertical tube of the same form as the column which it serves to carry. The connexion of the plate with this tube is strengthened by shoulders. The base-plates are set with their length north and south; and at right angles thereto, in such of the columns as serve as drain pipes, are two sockets, into which cast-iron pipes 6 inches in diameter are fixed, for conveying the rain water into drains of large size situated in the centre and at the east end of the building, which in their turn convey the water to the main sewer in the Kensington Road; the natural slope of the ground giving a sufficient fall to the pipes. At the upper portion of the tube of the base-plate are four snags, or projections with holes in them, corresponding with those at the foot of the column. The upper face of the tube and the under face of the column were all turned in a lathe so as to fit precisely without any packing; bolts were then dropped through the holes in both, and were secured by nuts. It was only in those columns that served as water pipes that any packing was introduced, and in them

Fig. IX.

a piece of canvas smeared with white lead was put into the joint.

Fig. X.

The form of the column, which was suggested by Mr. Barry, is that of a ring, 8 inches in diameter, with four flat faces, about 3 inches wide, cast upon it on the outside. The thickness of the columns varies, according to the weight intended to be supported, from of an inch to 1 inch. These flat bands afford surfaces well suited for attaching the horizontal girders which support the galleries and the roof, and by adding to the sectional area of the metal, greatly increase the strength of the column.'

Those portions of the height of the columns which correspond in depth and position with the girders, form separate lengths or connecting pieces, and unite the lengths of columns of the different stories. The connecting pieces are of the same sectional form as the columns, and like them have projections at each end, which serve to support the girders, and are provided with holes, through which are passed the bolts which secure them firmly to the columns. These holes alternate with projections so formed as to clip others which are cast on to the ends of the girders, and in the centre of each projection is a small notch which receives an iron key or wedge, and prevents the two surfaces from sliding upon one another. These arrangements will be explained more minutely hereafter.

The cast-iron girders, attached to these connecting pieces, serve to support the gallery floor. These girders are all 24 feet long, and 3 feet deep, and the upper and lower flanges or tables have a T-formed sectional area; the section A, Fig. XI, being 5.31

inches, and B, 7.64 inches. The rectangular space between them is divided into three equal parts by uprights having a + form of section, and the three rectangular spaces thus obtained are filled in with diagonal struts in each direction. The girder thus forms a double truss, in (1) In a Lecture on the construction of the building, delivered on the spot by Professor Cowper, of King's College, London, 31 December, 1850, a striking experiment was shown to illustrate the great strength of a hollow tube. Two pieces of quill, each one inch long, were placed in a vertical position between two boards, the upper one being adjustable by hinges: weights were then placed on the upper board just above the quills, until they reached 2:4 lbs., which was found to be the crushing weight.

which the diagonal braces are subject both to compression and tension. At the top and bottom of the end standards are small projections, as already noticed, by which the connecting pieces hold the girders, and at each end of the flat portion of the top and bottom rails are small sinkings, by which the girder is keyed up to its position. The flat portions of the upper and lower flanges of the girder are swelled out in width from the ends towards the centre, to increase the weight of metal in that part where the strain is greatest. In those parts of the building where no gallery was to be supported, the girders were cast with a less weight of metal, but the form was the same.

The first column was erected on the 26th September. The different castings were carried on with steady perseverance, and were sent from Dudley to the works as fast as they were executed. Every casting as it arrived was carefully examined, weighed, registered, and covered with a coat of paint, and every girder was proved by means of a hydraulic press. For this purpose, each girder was swung by means of a crane into a very strong cast-iron frame, rather longer than the girder, the bottom of which was formed by two fixed beams, placed 8 inches apart, and supported a few inches above the ground. At each end of these a cast-iron standard was firmly bolted between them, and rose to a height rather greater than the depth of the girder to be tested: on the inner faces of these standards two shoulders were formed, which received the projections cast on the ends of the girder. Between the fixed beams below, at two points dividing the whole length into three equal parts, were placed two 3-inch cylinders with rising pistons connected with a forcing pump by a strong metal tube. A girder being placed in this frame in an inverted position, the force-pump was worked until the pistons underneath the girder carried it off its lower bearings, and pressed it upwards against the shoulders by which it was firmly held, and the pressure was then continued until a strain equal to 15 tous was produced upon the girder, or twice the weight which it would have to sustain when fixed,' In this way the testing strain was made upon each girder, precisely at those points and in the same manner as the load from the gallery or the roof would do when the girder was in its appointed place. A self-adjusting apparatus, attached to the hydraulic press, indicated when the test strain of 15 tons had been applied. This apparatus consisted of an iron cylinder 14 inch diameter, communicating with the pipe which connected the pump and the press; so that the pressure obtained in it was, in proportion to its diameter, the same as that in the large cylinder; and it was fitted with a piston rod working in a vertical direction. Attached to this piston-rod was a lever, from the end of which a scale-pan was suspended, at a distance from the fulcrum ten times greater than that of the point of attachment of the piston from the same. The weight of the scale-pan and lever were balanced by a large mass of iron at the other end. A weight was placed in the scale-pan proportioned to the proof required; and the pump was worked until the water rising in the iron cylinder forced up the lever, and with it the weight attached, thereby indicating that the pressure had been attained.

Near the proving apparatus was erected one of Mr. Henderson's patent Derrick cranes, by which instrument every girder was raised from the wagon in which it arrived, placed on the weighing machine, weighed, removed to the proving press, tested, raised again and placed on the ground in a stack in less than four minutes. This crane consists of an upright mast E, Fig. XIV., kept steady when in use by two sloping stays FF, Fig. XVI. These stays are fixed in horizontal timbers on the ground, connected with the foundation plate H on which the mast turns. At the foot of the mast is a combination of wheels and handles for raising the weight, technically called a crab. A beam A, called the derrick, working at the bottom in a socket B, Fig. XVII., fixed to the foot of the mast, but hanging out from it in a sloping direction, is the chief peculiarity of the crane it can be raised more to the upright line or lowered to slope more outwards by means of the chain c. By this contrivance a weight may be raised from or deposited at any point

(1) In one case, the pressure was continued beyond the proof weight of 15 tons, in order to see what amount of strain the girders would bear without fracture: it was found that a strain of 30 tons produced no injurious effect; but the girder broke with the additional weight of half a ton.

(2) This weight was thus determined :--the diameter of the lever cylinder being 14 inch, and that of each of those in the proving frame 3 inches, the rams in the latter presented 8 times the surface of that in the lever cylinder; which being multiplied by the difference of length of the two parts of the lever, determined the weight for the scale-pan to beth of that to which it was desired to prove the girder.

ing, which had hitherto been so necessary and prominent a feature in all the operations of the builder. There was, however, a most efficient scaffolding in the parts of the structure itself, for as fast as these were erected they formed a scaffold for the superstructure. In raising the columns upon the base pieces, two poles were placed upright: these being connected by a horizontal piece, formed what is called shear-legs; the whole being steadied in its position by ropes from the summit to the ground. 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-pieces, and screwed up. When two columns had been fixed, a connecting piece was attached to each end of the girder, which was raised by the same means and fixed on the top of the columns: bolts were then 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 24 feet, and another pair of columns and a girder being similarly raised, the two sides of a 24-feet bay were thus formed. The four sides being completed, the square bay became a firm, self-supporting

structure; and by a repetition of these operations, all the smaller avenues of the building were erected of the different heights of one, two, or three stories. As many as 310 columns have thus been fixed in one week.

As the cast-iron girder, Figs. XX. and XXI., forms so essential and important a part of the structure, we may with advantage describe it a little more minutely. "The first and most obvious duty of the girders is to support the roof, but their second and equally

Fig. XVIII.

SHEAR-LEGS.

important duty is to give lateral stiffness to the whole structure. A girder of any form, provided its strength were sufficient, would have served to carry the roof, and might merely have rested on the top of the columns; but this would have given no lateral stiffness to the building, which might then have been levelled with the ground by the first storm. The contractors, therefore, in place of devising separate and independent means of supporting the columns and preserving their perpendicularity, adopted the plan of distributing the metal of the girders in a form which should possess a much greater depth than is usually employed in cast-iron girders; and then, by firmly connecting the top and bottom of each girder to the columns, they at once obtain the desired result. The columns and girders thus connected, may be compared to an ordinary four-legged table, in which the side-rails, which support the upper surface, are firmly fixed to the legs. A want of comprehension of this effect of the girders was the cause of a great waste of criticism on the presumed weakness of the structure."1

(1) "The Building erected in Hyde Park for the Great Exhibition, illustrated by 24 large folding Plates, embracing Plans, ElevaVOL. I. d