120 



HOTHOUSE-BUILDING. 



which the ribs are set in cast-iron 

 sockets. The framework, if we may so term 

 it, is composed of 9-inch wrought-iron 

 ribs, 12 feet 6 inches asunder, and 42 feet 

 long, in lengths of about 12 feet, and 

 welded together, and brought to the 

 required curve. The top part of these 

 lower or main ribs is supported by cast- 

 iron tubular columns, which also serve 

 as footing for the bottoms of the ribs, 

 constituting the upper part of the centre 

 division, as well as to support the bearers 

 for the balcony which is extended round 

 the centre division of the house, and 

 which is reached by two elegant spiral 

 stairs. A continuous curb of the same 

 scantling as the ribs connects the column 

 heads, vide figs. 118 and 119. " "The 

 whole of the ribs are braced together, and 

 strutted by wrought-iron tie-rods, pass- 

 ing through cast-iron tubes, which act as 

 purlins. These purlins, or connecting 

 bars between the ribs, are new in con- 

 struction : they are formed of a small 

 1^-inch round bar, welded in long 

 lengths ; and, passing through the ribs, 

 they form a continuous tension-rod all 

 round the house at each purlin, (which 

 are 9 or 10 feet apart,) with means of 

 straining them as tight as possible. This 

 tension-bar is enclosed within a tubular 

 bar of wrought-iron, exactlyfitted between 

 the ribs, acting as distance-pieces in op- 

 position to the strain of the tension-bars. 

 This knits the entire structure together." 



Fig. 



The upper roof of the centre part is 

 supported, as has been already noticed, 

 by 20 tubular cast-iron columns, ten on 

 Fig. 118. Fig. 119. 



each side, in a line with the sides of 

 the wings. These columns carry down 

 the rain water collected in the gutter of 

 the upper roof into tanks formed round 

 the whole of the interior of the building, 

 as shown at a a a a in transverse section, 

 fig. 120, and at e in fig. 121. The water 

 from the lower roof is received into the 

 120. 



