POLMAISE METHOD OF HEATING HOTHOUSES. 



63 



who is equally fond of it, though with less means, will inquire 

 first, Can I grow more cheaply? While the grower for profit 

 will consider both of equal importance. I will consider cost, 

 and first the original cost : this will be regulated by the purpose 

 for which it is required, similarly to other heating powers. An 

 apparatus of equal power with mine may be erected for 20/., de- 

 pendent on the price of brick and slate. It must be considered that 

 for tins sum a great amount of bottom heat is secured, from 82° to 

 94° Fahr., over a bed 22 feet 6 inches by 9 feet wide, together 

 with the requisite amount of atmospheric heat in a house 28 feet 

 by 17. Compared to hot water, lam sure the first cost does not 

 exceed one-half what the latter would be to secure the same 

 amount of bottom and atmospheric air in the same house in the 

 same locality. But the way in which the economy is best 

 viewed is by considering that the entire expense of the distri- 

 bution of the heat is necessarily saved by the air distributing it 

 by its own motion, and that the expense of the air-boiler and 

 setting is about the same as the water-boiler and setting ; the 

 expense of the tank it is fair to charge not to the heating but to 

 the evaporation, as moisture must be supplied in some way under 

 any mode of heating. 



The working economy I take to be equally certain. If the 

 stove is properly built, there need be but little loss of heat, the heat 

 of the stove being all swept into the house by the currents, ex- 

 cept that portion which is lost at the junction of the stove with 

 the external wall of chamber ; while in the hot-water apparatus, 

 if the boilers are set externally (and it has not been found ad- 

 visable to set them within the house), there is great waste of 

 heat, — I do not speak of every individual case, but of the gene- 

 rality of cases ; and since a given quantity of fuel can only evolve 

 a given quantity of caloric during its combustion, it is quite 

 evident that that system must prove most economical in the use 

 which secures the most caloric for the purpose required. With 

 regard to the amount of caloric passing up the chimney, Pol- 

 maise stands on the same footing with all other economical 

 stoves in which the combustion of the fuel is regulated by the 

 supply of the oxygen and by means of Sylvester doors, and 

 dampers in the chimney ; the amount of heat lost in this manner 

 is inconsiderable. Some heat must always be sacrificed in this 

 manner in all systems ; for if there were no caloric in the chim- 

 ney, — that is, if the air in the chimney were not rarefied, there 

 would be no current of air to the fuel, and the fire would not 

 burn ; and if this is to be saved, it can only be done by bringing 

 the chimney through the house, — in fact, by again returning to 

 the flue system. 



The next advantage I shall notice is the equal distribution of 



