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 bottom 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 maybe 

 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 Encyclopaedia 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 wa3 that he 

 made the application of the troughs in the pits he designed, as described at 

 page 3G3 of the present treatise. 



