PLANTS, WITH GLASS ROOFS, 



191 



Paxton, to whom the merit of this mode of roofing is entirely due, 

 has also adopted an improvement in the construction of the sash -bar, 

 viz., having grooves for the panes instead of rebates (see figs. ]30 and 181) ; 

 the advantages of which grooves are, 

 that lees putty is required, and that what 

 is used does not so readily separate from 

 the wood, and thus admit the wet between 

 the wood and the putty. The roofs of 

 such houses are entirely fixed, and venti- 

 lation is effected either by having the 

 perpendicular ends of the ridges moveable 

 Fig. 130. Section of an on hiuges, or by the front glass and ven- 

 iron sash-bar, with ^jjators in the back wall. The expense 



grooves for the glass. - 3 ^ 



of this mode oi rooting is doubtless greater 

 than by the common flat mode, but not so much so as might 

 be expected, because the sash-bar can be formed lighter, and ^'f/j^^ 

 where crown-glass is used the panes may be much smaller, with grooves for the 

 For plant-houses the advantage of admitting the sun's s^'"**- 

 rays perpendicularly, early in the morning and late in the afternoon, will 

 much more than compensate for any additional expense. In an archi- 

 tectural point of view, the merits of this mode of roofing are perhaps as 

 great as they are with reference to culture : the roofs being lower, are less 

 conspicuous, and the common shed-like appearance is taken away by the 

 pediments which form the ends of the ridges, and appear in a range as a 

 crowning parapet to the front glass. Indeed, if it were desirable, the tops 

 of the ridges might be made perfectly horizontal, and all the slope that was 

 necessary for carrying the water from back to front, or to both the sides, 

 given in the gutters between the ridges, as is done in roofing common 

 buildings of great width. Fig. 132 is a perspective view of a house 



