Greenhouses and Hothouses. 253 



over the lower stratum, and thus ascend regularly from the 

 surface to the roof, and here, the effects of the law which 

 tends to bring all bodies to an equality of temperature prac- 

 tically fails in forcing-houses. Air, in itself, possesses com- 

 paratively little capacity of conducting its contained heat, 

 and hence the great practical disadvantages of Polmaise. 

 If air possessed the same power of conduction as water, 

 then hot air would be superior to hot water in every respect, 

 because the atmosphere of a house could be equally heated 

 throughout by direct communication with the source of heat, 

 without the intervention of water ; this latter element serving 

 only as a conductor, imparting its latent heat to other bodies 

 from which it is radiated more equally over the lower surface. 

 Upon what foundation the advocates of hot air assert, that it 

 is the most natural method of warming hothouses, I am 

 unable to discover, and would be glad to learn. Perhaps I 

 may be answered : We conduct the hot air into the house by 

 channels or drains under ground? Very good, but then Pol- 

 maise has no conductors, it denies the use of them, and this 

 is exactly how it obtained its name and notoriety, and 

 wherein it is different from others. Suppose, however, you 

 keep the drain system without the name, (this is Meek's 

 improvement,) I would like to know, first : where is the 

 advantage of having under-ground drains? and secondly: 

 where is the original econony? These, Mr. Editor, are 

 practical questions ; let them not therefore be obscured by 

 sophistry, or shuffled over by equivocation, for upon them is 

 built the whole fabric of hot-air controversy. 



Let us consider briefly the utility of under-ground drains 

 or flues. The?e, we are now told by the advocates of hot 

 air, are absolutely necessary for an equal distribution of 

 heat over the house. The air is thus impelled by its in- 

 creased rarity through these subterraneous caverns, until it 

 finds an exit at their extremity, which communicates with 

 the house. These are nothing more nor less than buried 

 flues, — flues sunk in the ground, after the fashion, (now 

 almost obsolete,) that some very old houses are heated upon ; 

 and every gardener knows full well the difficulty of heating 



