174 HEATING BY HOT WATER, HOT AIR, AND STEAM. 



between these two points, by means of water, that it does 

 through the medium of air, i. e., by direct communication, in 

 each case the calorific action being in pretty exact ratio to the 

 combustion, and both acting under the most favorable circum- 

 stances. This would, at first view, decide us in favor of hot 

 air as a means of heating, in preference to hot water ; and the 

 fact that the heat becomes more rapidly sensible by hot air, has 

 induced many to come to a premature conclusion on this point. 



Let us, however, take another view of the position here 

 alluded to, and consider the two methods in regard to their per- 

 manency of heating power. We find also, by calculation, that 

 while the temperature of the house is maintained at 60° for 

 3-25 hours by hot air, with the same amount of combustion the 

 temperature of 60° is maintained for 10 hours by hot ivater, or 

 three times the period that the equilibrium is maintained by hot 

 air. The same experiment shows that 2 bushels of coal will 

 warm an equal volume of air in a hot-house the same length of 

 time that 5-067 bushels will warm by direct connexion of its 

 particles with the source of heat. 



Now, in a la-rge house, or number of houses, this saving of 

 fuel would, in a few years, amount to the difference of cost be- 

 tween the two apparatuses, keeping out of the question the saving 

 of labor, the cleanliness and neatness of the one compared with 

 the other. In regard to these numbers, we may remark, that 

 the calculations of some experienced and intelligent gardeners, 

 drawn from accurate observation, have made the difference be- 

 tween the two methods still greater, in regard to the consump- 

 tion of fuel, — placing this position in still stronger light than by 

 the calculation here given. 



This remarkable difference in the retention of heat is owing 

 to the following causes. 



First. The power possessed by the water [as already ex- 

 plained, see " Comparison of Water and Steam "] of absorbing 

 and retaining a large amount of heat, and giving it off gradually, 

 as the atmosphere requires it. 



Secondly, Owing to the body of metal with which the water 

 is surrounded, which also absorbs and retains a large amount 



