ON THE CONSTRUCTION AND HEATING OP HOT-HOUSES. 
257 
gardeners there calculate the inclinations or angles of their houses from the base or 
horizontal line of the quadrant, and not from the perpendicular, as the English gar- 
dener. Both systems are equally good when understood : but an understanding is 
requisite, because an angle of 70 degrees, which with us is well known to be a very 
flat roof, is with the French very steep, and the same slope as our 70, on their 
system, is an angle of 20 degrees ; likewise an angle of 15 degrees, which in our 
calculation is very steep, only fit for early peach houses, and other fruit houses, 
where the trees are trained to the back wall, is by the French calculation very flat 
and unfit for early forcing. See the angle of 15 in the annexed scale. 
3 6 9 12 feet 
An example or two will probably explain the subject better than words. Sup- 
posing a house for early forcing was required to be built, 12 feet wide, and the roof 
to form an angle of 55 degrees. Now to accomplish this, it would be necessary to 
raise the back wall as much as 17 feet higher than the front, as a b. Again, a 
house of the same dimensions, with an angle of 45 degrees, the back wall would 
require to be 12 feet higher, as a c. With an angle of 35, only 8 feet, 4 inches 
higher than the front, a d. With an angle of 20, only 4 feet, 4 inches higher, a e. 
With an angle of 10, which is the usual slope of frames, only 2 feet, 2 inches. 
Of course, houses of less width require less elevation at the back, to give the 
required angle ; for instance, a house 6 feet, with a roof at an angle of 45 degrees, 
will only need the back wall to be 6 feet higher than the front. Also a frame, 3 feet 
VOL. II. NO. XXIII. L L 
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