52 



POLxMAISE METHOD OF HEATING HOTHOUSES. 



the distance from the heating body increase, it is utterly impos- 

 sible that the earth can be equally heated by radiation, and we 

 know practically that it is not, but that we have a sphere un- 

 equally heated on its surface, this sphere enveloped by an 

 atmosphere, itself consequently unequally heated. And what is 

 the result when liquids or gases are unequally heated in different 

 portions of the same mass ? That currents are established for the 

 purpose of restoring the equilibrium ; that till the equilibrium be 

 restored they are ceaseless ; that the force or velocity of such 

 currents mainly depends on the difference of temperature between 

 the two portions, the result being that the portions which are 

 too hot become cooled, and those too cool become warmed. 

 And but for this principle a considerable portion of the earth's 

 surface would be uninhabitable. The unequal heating causes 

 the current, the current diffuses the heat ; they are antagonizing 

 forces : thus the atmospheric variation is the cause of the trade 

 and other winds, while these put a limit to the variation itself. 

 Nature's principle of diffusing atmospheric heat clearly therefore 

 being, the internal movement of the atmosphere itself. We 

 have, therefore, a body radiating heat, a body absorbing it, an 

 atmosphere unequally heated ; this very inequality the cause of 

 sufficient distribution. How beautifully simple are Nature's 

 means ! how perfect her results ! He who created the different 

 forms of matter endowed each with properties exactly fitting it 

 for the purposes it would have to perform. To heat a liquid to 

 warm the air (a gas) was no lesson of His teaching ; it was man's 

 error, who, neglecting to study the vast book set before him in 

 the kingdoms of Nature, has used an instrument for a purpose 

 for which it was never intended, and is therefore full of prac- 

 tical imperfections ; and surely we shall find that the true prin- 

 ciple of diffusing heat artificially is to provide a radiating body, 

 namely, the burning fuel ; an absorbing body, such as an iron 

 plate, over which the air we desire to heat can freely move, and 

 this is Polmaise ! 



I shall now prove its truth by reference to our present state 

 of scientific knowledge, and see how far it is in accordance with 

 the laws which we know regulate the diffusion of heat through 

 different forms of matter ; and having shown it a natural mode, 

 I shall have little difficulty (as might be expected) in proving 

 that it is philosophical and sound in principle. I leave the 

 question of the production of heat entirely ; a given quantity of 

 fuel will evolve in its combustion a given quantity of caloric. 

 The country is deeply indebted to Dr. Arnott for pointing out 

 the true principles on which the caloric evolved should be 

 economized, and its production regulated ! The combustion (and 

 consequently the caloric) should be regulated, not by the supply 



