56 



POLMAISE METHOD OF HEATING HOTHOUSES. 



at once of the absurdity of such a combination, for on this plan 

 it is evident we can only supply much heat with much air, while 

 probably only a small amount of the latter is requisite. I should 

 even say that the wants of a hot-house, with regard to air and 

 artificial heat, were frequently the one exactly the reverse of the 

 other ; that in the depth of some winter's night, with a cutting 

 wind blowing, the requirements of the hot-house as regards heat 

 would be great, while it would experience no want of fresh air. 

 Again, experience has proved to us that plants will flourish in 

 extreme beauty elsewhere than in the open air ; and while glass 

 houses may be considered as evils rendered necessary by our 

 climate, these have proved to us that with a certain amount of 

 ventilation plants will flourish within them. Is it not then the 

 most rational and most economical course to ascertain the amount 

 of air required to keep plants in health, and then to provide the 

 means of heating that air? Is it not wasteful to heat more air 

 than the plants require, to be obliged to heat a quantity of cold 

 fresh air, and blow it through the house incessantly, only for the 

 purpose of keeping up the heat, when the air already in is quite 

 sufficient for a time, and probably only wants one quarter the 

 heat to raise it to the required temperature that the external air 

 needs? I well know that the best practical horticulturists allow 

 a great amount of ventilation (some even by night), and with the 

 best results ; let it be freely provided ! But let us not so com- 

 bine ventilation and heating, that when one is wanted the least 

 we must supply it the most. Another objection to this mode of 

 heating is, that as the escape of that air which is to allow fresh 

 warm air to enter takes place at the roof, the flow of hot air is at 

 once determined to the very point to which it is probably not 

 required, and thus a thermometer on the floor and another in the 

 roof would indicate considerable variation of temperature ; in 

 other words, the heat is not equally diffused, the agitation of the 

 mass is not complete ; it arises from an extraneous force, and not 

 from a movement within ; the one may be aptly compared to the 

 motion produced among the particles of a liquid by a stream 

 running through it, the other the motion arising from internal 

 fermentation. 



But let us turn from error to the truths of Polmaise. Nature 

 teaches us that the only way to heat air is to bring it in contact 

 with a heated surface, — Polmaise does so. Philosophy tells us 

 that the most rapid means of diffusing heat is to employ that 

 medium which moves with the greatest rapidity, namely, the 

 air, — Polmaise does so. Economy tells us that an agent is an ex- 

 pensive luxury ; he takes his per centage ; that we do not require 

 his services, nay, they are an obstruction ; that our course is to 

 allow the air to diffuse the heat itself, and to warm that air which 



