CONSTRUCTION OF THE BUILDING.

63

“ thoroughly washed, the water at once disappears between the openings, and the Conclusion of“ boards become almost immediately fit for visitors.” construction or

Having now endeavoured to furnish the reader with sufficient detail of a small ° e 4 eet bay ’portion of the building, to enable him to use it as a scale, whereby to estimatethe quantity of labour represented by a structure of the general dimensions we General aimen-are about to enumerate, it may be stated that the total area of the ground floor is twes. and q "“'*772,784 square feet, and that of the galleries 217,100 square feet. The galleriesextend nearly a mile in length. The total cubic contents of the building areabout 33,000,000 feet; there are nearly 2,300 cast-iron girders, and 358wrought-iron trusses for supporting the galleries and roof, 30 miles of guttersfor carrying water to the columns, 202 miles of sash bars, and 900,000 superfi-cial feet of glass. The width of the nave is, within 10 feet, double that of St.

Paul’s Cathedral , whilst its length is more than four times as great.

With a general knowledge of the construction of the nave, we may imaginethe visitor, returning to the transept, better qualified to enter into the mecha- The transept,nical details, and the amount of difficulties presented to his notice, by that greatfeature of the building. The arrangement of the vertical shafts, galleries, &c., issimilar to that of the nave ; the main points of difference commencing at the levelof the flat roof. It will be remembered that the spaces to be covered at a height of its roof.

64 feet from the ground, are, firstly, a main avenue, 408 feet long by 72 feet wide;and secondly, two aisles, each 408 feet long by 24 feet wide. It was determinedthat a semi-cylindrical vault should span the larger of these areas, and for thatpurpose semicircular ribs (see Plate I.) extend from side to side, their ends beinginserted into the hollow columns, whilst they are steadied by the insertionbetween, and at right angles to them, of stout timbers, 9 feet 2 inches from oneanother, acting as purlins.

The structure of the ribs is shown in fig. 14. To quote from a paper descrip- Construction oftive of the building, read at the Institution of Civil Engineers , on the 14 th of transept roof.January, 1851, “ they are made in three thicknesses of timber, cut into segments, Description“ 9 feet 6 inches long, of a circle of 74 feet extreme diameter, the centre thickness “ Transactions of“ being 4 inches by 131 inches, and the outer, or flitches, breaking joint with the am Engineers.”“ centre, being 2 inches by 131 inches. The flitches are nailed to the centre“ thickness, and fths inch bolts, about 4 feet apart, on the segment, traverse and“ bind together the three thicknesses. On the extrados, or outer circum-“ ference of the wooden arch thus formed, two planks serving as a gutter board“11 inches by 1 inch, and a bar of iron 2 inches by fths inch, are bent to the“ curve; and on the intrados, or inner circumference, a piece of timber, 7 inches“ by 2 inches, moulded to correspond with the form of the columns, and a bar of“ iron, 31 inches by fths inch, are also bent to the curve. Bolts, at intervals“ of 2 feet from centre to centre, passed through the depth of the rib, unite these“ additions to each other, and to the main rib, which, thus increased in scantling,

“ measures, complete, 1 foot 6 inches by 8 inches.” In order to perfectly con-The transept roof,nect these ribs, so that any force exerted, by wind or other causes, tending to h ° w constrllcte 'the displacement of any one of them, may be distributed over the whole mass,iron rods have been set diagonally, forming a complete reticulation over thewhole inner surface of the roof. The main ribs are fixed spanning the transept,at intervals of 24 feet from centre to centre. Each of these 24 feet widths isdivided into three parts, and at 8 feet from one another, and from the main ribs,minor ribs are introduced. Between them again, but being semicircles of larger