Greenhouses and Hothouses. 251 



embrace the quantity and the quality of the heat generated. 

 It has been ascertained by calculation, that the atmosphere of 

 a hothouse receives three times as much heat from a certain 

 quantity of fuel, through the medium of hot-water pipes, 

 than from a Polmaise stove, and nearly twice as much as 

 from a common flue, or, in other words, the atmosphere of 

 the hothouse will receive as much caloric from one bushel of 

 coal, by a hot-water apparatus, as it would from three bush- 

 els, by a Polmaise stove, or two bushels, by a common flue. 

 These calculations may not be found to hold good in every 

 series of similar experiments, owing to the difference of cir- 

 cumstances of the constructing and working of the various 

 apparatus, which, by the mere plan of their erection, as well 

 as by the extent of surfaces of radiation, may considerably 

 affect the results ; but, under general conditions, these calcu- 

 lations will come pretty near the truth, and, in some in- 

 stances, the difference of consumption is much greater in 

 favor of hot water. I have seen seven houses heated effectu- 

 ally by one fire and boiler, and consuming no more fuel than 

 one single house heated by Polmaise. At one time, I man- 

 aged four houses heated by one fire and boiler, and requiring 

 less fuel than a common furnace in an adjoining vinery, 

 heated by a brick flue. There can be no doubt, that for 

 economy of fuel, a well-constructed hot-water apparatus 

 stands first ; next, a common smoke-flue ; and lastly, Pol- 

 maise, or, properly, hot-air heating. 



The quality of the heat generated may be said to be alike 

 in all cases, although the temperature at which the heated 

 air is radiated from its source has a considerable influence on 

 the atmosphere of the house, and hence, when we speak of 

 the quality of heat, we mean, that in some cases, as in old 

 flues and in Polmaise stoves, other gases than those which 

 compose pure atmospheric air enter the house from tlie fire ; 

 close, well-built flues, however, generate heat as pure in its 

 properties as hot-water pipes, and the warmth of the one is 

 not more arid than the other, although the contrary is sup- 

 posed by many to be the case. 



When we raise the atmosphere of our hothouse above the 



