MECHANICS AND USEFUL ARTS. 5 



and screw. The second tier of columns \vas then fixed in precisely the 

 same manner on the connecting pieces ; and thus were securely joined 

 the girders throughout the building. The peculiar action of the con- 

 necting pieces, however, should be further explained. The projections, 

 or " snugs," upon their upper and lower portions, act not only as 

 brackets, but likewise hooks ; those on the lower ends bending upwards, 

 and those on the upper ends downwards, so as between them to grasp 

 the end struts or standards of the girder. To retain the girder in a 

 vertical position, and prevent any lateral movement, its bottom and face 

 have a tenon, which drops into a mortice-hole in the projection of the 

 connecting piece ; while the top end face of the girder, over which the 

 upper connecting piece hook extends, is grooved to correspond with the 

 projection, and the two surfaces are keyed together by a piece of iron. 

 This system of attaching the girders to the projections of the connect- 

 ing pieces has proved very successful. The principle of the ridge and 

 valley roof, as applied by Mr. Paxton to horticultural buildings, was 

 well adapted from its extreme lightness to buildings of great extent, 

 the whole roof of the exhibition building weighing only upon an aver- 

 age 3^ Ibs. per superficial foot. This was the result of the subdivision 

 of surface in the light frame-work and rafters. From a roof of such 

 light construction it became important to convey away the rain-water 

 as soon as possible ; for it is estimated that were a quantity of water, 

 one-eighth of an inch in depth, suffered to remain upon the roof, an 

 additional pressure of 275 tons, for the time being, would be the con- 

 sequence. This is prevented by means of cambered or curved beams 

 of wood, which divide the roof into spaces of eight feet each, and are the 

 gutters into which the water runs from off the glass roofs, which slope 

 into them on either side. These cambered gutters run longitudinally, 

 and their entire length is no less than 34 miles. These lines of gutter 

 were made in 24-feet lengths, each cambered upwards, so that the 

 water in the gutter has only to run down one-half its extent, and thus 

 off the roof at one end of the furrow, where it discharges itself through 

 a casting into a second and larger gutter lying transversely to the first, 

 and resting upon the roof girders. The fall of the smaller gutter on 

 either side is 2^ inches in 12 feet, or 1 inch in 4 feet 9 inches ; so 

 that the water is at once drained into the larger gutter, and thus con- 

 veyed to the hollow columns before it can accumulate at any one point 

 throughout the building. Xot only is the roof drained externally in the 

 manner described, but small channels are provided in the longitudinal 

 gutters to carry off the condensed vapor from the interior surface of the 

 roof. 



The glazing of this vast roof was executed in the following manner. 

 The sash-1 jars, having been painted, were received upon the roof, where 

 both then* grooves were filled with putty, as was also the rabbet in the 

 ridge, and the sill in the furrow ; the side edges of the pane were then 

 inserted in the bar grooves, and the glass thus framed at the sides was 

 laid in its place, prised up by the workmen into the ridge, and fastened 

 at the lower end by a nail driven into a drilled hole in the bar ; but 

 the larger sash-bars were fastened into the ridge by dowels. As the 

 glazing required to be executed in a very short time, " glazing- wagons ' ! 



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