258 ON THE CONSTRUCTION AND HEATING OF HOT-HOUSES. 
wide, having an angie of 10 degrees, would only require the back to be 7 inches 
higher than the front. 
It will always be useful to remember that a perpen- 
dicular equal to the width of the house always gives an 
angle of 45 degrees. Say g h is the width of the house, 
the perpendicular line or back wall, i, is equal in height to 
the width of the base, g h, which gives the angle of the 
roof, Jc, 45 degrees. 
The English gardeners calculate inclinations from the perpendicular, which m 
drawing plans for building may be explained by the annexed scale, wherein the 
0 3 6 9 12 feet 
side, B, of the quadrant is made the base instead of A, which of course reverses 
the whole order of calculation, making the first inclination 85 instead of 5. Sup- 
posing it is desired to build a house 12 feet wide, 
with the angle of the roof 35 degrees, the elevation 
of the back wall must be precisely the same as in 
the French scale is required for 55, viz.,— 17 feet 
higher at the back than the front, as a b ; the same 
angle, 9 feet wide, the back 12 feet eight inches 
higher than the front, as c d ; if only 6 feet wide, 
the back need only be 8 feet 6 inches higher than the 
front, as ef; and so on in proportion, measuring 
according to the annexed scale. 
