HE plan forms a parallelogram, 1,848 feet long and 408 feet wide, besides a projection on the north side, 48 feet wide and 936 feet long. A main avenue, 72 feet wide and 66 feet high, occupies the centre through the whole length of the building. Flanking this on either side are smaller avenues alternately 24 feet and 48 feet wide; the two first on either side of the centre are 43 feet, and the remainder 23 feet high. About the centre of the entire length, at a point determined by the position of a row of large trees, which it was resolved to inclose, these avenues are crossed by a transept of the same width as the main avenue, or 72 feet, and 108 feet high; two other groups of trees on the ground give occasion for open courts, which are inclosed within the building. The area thus inclosed and roofed over amounts to no less than 772,784 square feet, or about 19 acres;[[4]] the building is, therefore, about four times the size of St. Peter's at Rome, and more than six times that of St. Paul's, London. Three entrances lead to this vast interior, one in the centre of the principal or south front, and one at either end of the building. The number of these is necessarily small, in order to facilitate the arrangements for the money-taking, and to avoid having too large a staff of officers; on the other hand, it was equally desirable to afford the most ample opportunities of egress for visitors, and accordingly fifteen exit doors are placed at frequent intervals.
GROUND-PLAN OF THE BUILDING.
| A. Principal Entrance. B. West Entrance. C. East Entrance. D. Refreshment Courts. | E. Entrance. F. Gentlemens' Ante-rooms. G. Ladies' Ante-rooms. H. Pay Place. | I. Accountant. K. Exits. L. Ante-rooms. M. Committee Waiting-room. | N. Royal Commission. O. Clerks. P. Stairs. Q. Engine House. |
It will be well to mention here that the horizontal measure of 24 feet, which we have seen as the unit in the plan of the Building Committee, is also preserved in the present plan; every horizontal dimension of which is either a certain number of times or divisions of twenty-four feet.
The avenues into which the plan is divided are formed by hollow cast-iron columns twenty-four feet apart, which rise in one, two, and three storeys respectively, to support the roof at the different heights given above; in the lower storey these columns are nineteen feet high, and in the two upper ones seventeen feet. Between the different lengths of the columns short pieces are introduced, called "connecting-pieces," from the office they perform; these are three feet long, and are so contrived that they serve to support girders in horizontal tiers, dividing the greatest height into three storeys as already mentioned. The girders, of which some are of cast and some of wrought iron, are all of the same depth, namely, three feet, with the exception of four, to be specially named hereafter, and by this arrangement the same horizontal lines are preserved throughout the whole of the building. They are also all similar in appearance, forming a kind of lattice-work, by which construction they do not look too heavy for the slight supports; and large solid masses are avoided, practically showing how great strength may be combined with elegance and lightness. The first or lower tier of these girders, in parts of the building more than one storey in height, forms the support for the floor of the galleries, which are twenty-four feet wide, and extend the whole length of the building in four parallel lines, intercepted only by the transept, round the ends of which they are continued. Numerous cross galleries connect each pair of longitudinal lines on either side of the centre avenue, which remains uninterrupted from end to end, and can only be crossed on the gallery-floor at the extremities.
These galleries are reached by eight double staircases, of easy ascent and ample width, which are placed between the lines of gallery so as to communicate equally readily with either, and are so distributed as to give two to each quarter of the building; in the eastern or foreign half two supplementary staircases of smaller dimensions have been added.
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.
VIEW OF ONE 24-FEET SQUARE BAY OF ROOF PARTLY COMPLETED.