PLATE XXII. 
sash of a roof, strengthened by two iron bars, to prevent its sagging, on account of its length, the 
short head sash should have one. At F, is part of such a treillage as is placed against a back wall. 
H I represents a right lined wall. K L beneath it an angular one. All the rays proceeding from the 
sun, at m, are seen to illume every part of the first, while no more than one half of the last is en¬ 
lightened by them: that part only between the figures 6' and 7, directly opposite the luminary, is with¬ 
out shade ; and the shadows projected by the several angles towards L are seen increasing as they are 
more remote from it. In this scheme the sum of the shades will be found equal to the sum of the en¬ 
lightened parts ; but if the plate would admit of its being continued, they would by far exceed them ; 
and in that case the proportion would be the same, though the sun, atu , was placed as high as the plate 
would admit, in the line n produced : therefore this disposition is very disadvantageous in spring, 
when the sun is not far above the horizon, and his light as well as heat particularly wished for. At 
O (the top of the Plate), is the elevation of the angular wall drawn up from the plan, where what 
has been advanced is again made evident. 
