31 



showing the amount of boiler surface which must be 

 exposed to the fire to heat given lengths of pipe, res- 

 pectively 4 inches, 3 inches, and 2 inches in diameter. 



— (Johnson's Mod. Gard. Diet.) 



Heating by Hot Air. — Every system of heating is 

 more or less founded upon the fact that, if a hot body 

 be introduced into an enclosed room, the air in contact 

 with that body becomes lighter, and rises as it is 

 heated, is cooled and becomes heavier when it reaches 

 the upper part of the room, and consequently sinks 

 down to be again heated by coming in contact with 

 the hot body, and thus is kept in perpetual circula- 

 tion. This is the principle upon which all heating is 

 founded; yet no one, that we are aware of, ever 

 thought of making the air circulate at once over, and 

 be heated by the furnace direct, as suggested by Mr. 

 Murray, head gardener at Polmaise, and thence de- 

 signated the Polmaise system. Other persons have 

 always employed flues, or pipes, or tanks, heated by 

 a distant fire, to communicate the desired warmth. 



Mr. Murray deserves great thanks from horticul- 

 turists for the publication of his cheap mode of heat- 



