292 CULINARY GARDENING. BOOK I. 



being changed into manure. In some cases, it may also be 

 generated by the sun, (as in Dr. Anderson's patent hot-houses,) 

 and preserved in proper compartments, though probably in 

 very few situations. All modes may occasionally be employed, 

 or taken advantage of, in particular circumstances; but that 

 by fuel, furnaces, and flues, is the only plan capable of being 

 put in general practice with advantage. The greatest difficulty 

 that occurs with heat is its management, so as to retain and 

 regulate its degree agreeably to the nature of the climate to be 

 imitated. It is retained partly by having the house made as 

 nearly air-tight as possible, and partly by an inner curtain in- 

 vented by the author, which is let down during night immedi- 

 ately under the glass, and which, by preventing the heated air 

 of the house from coming in contact with the glass, permits 

 only a very small quantity to escape. It is preserved at the 

 proper regulation chiefly by this curtain, which, as it retains the 

 proper temperature, does not require the heat to be greatly 

 raised at the beginning of night in order that it may not be too 

 low in the morning, as is the case in all hot-houses where a cur- 

 tain is not in use. For be it observed here, that though the 

 house be perfectly air-tight, yet as glass from its porous nature 

 is easily permeable by either heat or cold, and consequently as 

 heated air always ascends to the top of the house, it must be 

 continually given out to the atmosphere through the roof as 

 well as sides of every glass hot-house. And this is the sole 



