316. FORCING GARDEN. 
Proper provision ought, however, to be made for prevent- 
ing more of the steam or vapor rising from the hot water 
(into the house) than what is requisite ; for, if this precau- _ 
tion be not adopted, there will be too much damp in the 
winter season for the proper growth or preservation of the 
plants.* 
To mention the rays of the sun amongst the sources of 
artificial heat may excite a smile; yet it happens that, 
from the stagnation of air, the reflection of light from 
walls, and other circumstances, they often produce a very 
considerable proportion of the increased temperature of a 
hot-house. This species of heat, however, is materially 
affected by the admission of the air necessary to the growth 
and healthy state of the plants. We are not aware of its 
having been employed as a primary,source of heat, except 
in the case of Dr. Anderson’s patent hot-house, in which 
heated air was kept, bottled up, as it were, in separate 
chambers; an arrangement too irregular and unmanage- 
able to be of much utility in our variable climate. 
Vegetable substances in a state of fermentation evolve a 
considerable quantity of caloric, and are much employed to 
produce dottom heat in hotbeds, pine-apple, or melon pits. 
* It will be seen that Mr. Rendle’s mode of heating is merely an exten- 
sion of that of Mr. Corbett, described above; and as some interest was ex- 
cited by Mr. Corbett’s claim to originality in his mode of heating, it may be 
proper to state that his patent was sealed in August, 1828, while the same 
mode, as described at page 362, was in operation in the gardens at Hopetoun 
House in October, 1832, two years before the publication of this treatise in 
the Encyclopedia Britannica. In the Gardener’s Magazine for 1830, a 
description is given of a house fitted up in the nursery of Mr. Knight, King’s 
Road, Chelsea, by. Mr. George Jones, of Birmingham, with cast iron troughs 
and movable covers, from which account Mr. Smith believes it was that he 
made the application of the troughs in the pits he designed, as described at 
page 363 of the present treatise. 
