ON THE CONSTRUCTION AND HEATING OF HOT-HOUSES. 
259 
It will also be seen, that hy this scale, 80 degrees is the common angle of a 
frame, and exactly corresponds with 10 degrees on the other mode of calculation ; 
and, therefore, of course requires the same elevation, viz., — 7 inches at the back 
e more than the front. For instance, say a b is the 
side of a frame, three feet wide, to obtain an angle of 
80 degrees, elevate it behind 7 inches, as at c, and 
'Tt 1- — I 1 the required angle is obtained. 
To find the angle of the roof of any hot-house, it is merely necessary to place 
the side A of the quadrant in a parallel line against the side of the roof, as .z for 
our way of calculation, and the side B for that of the French, and the plumb-line, 
hanging perpendicularly, will immediately give the required angle. 
To ascertain on what angle the roof of a house should be constructed, it is only 
necessary to know when the house will require the most light ; which, if a fruit- 
house, will be at the time the fruit is wanted to ripen, but if a plant-house, always 
in the depth of winter. It is a maxim adopted by T. A. Knight, Esq., to always 
give such a slope of roof as shall be at right angles to the sun's rays at the season 
when the fruit is wanted to ripen. Front sashes, however, render this rule not 
altogether necessary, as much light and sun is admitted through the front sashes in 
winter, and a somewhat flatter roof, than would otherwise answer, will do well for 
summer. 
All houses with plain roofs, and without front sashes, if they are wanted to 
produce fruit very early, will require a roof so steep that the sun's rays will fall 
perpendicularly on it early in the season ; but, if the house is made with front 
sashes, a roof about 60 or 65 degrees will do very well. 
All plant-houses should have front sashes, as a very steep roof is both unsightly 
and inconvenient for plants. 
An angled roof, like that of our large green- house at Chatsworth, figured page 
81, may have a very flat roof, and yet admit a deal of light. I apprehend that a 
house built on this principle, would produce fruit earlier than any other; and it 
certainly answers well for plants. 
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