6 1 TOLMAISE METHOD OF HEATING HOTHOUSES. 



the heat. Taking the word equal in its strictest sense, that 

 which is desired will never be absolutely attained ; but it is not 

 to be denied that the closest approximation to uniformity must 

 be secured by employing that medium which is most rapid in its 

 motions. But this excellence attaches to all systems where the 

 air is used as the medium of diffusion. What, therefore, is the 

 peculiar merits of Polmaise? If we again look to Nature, we 

 shall see a specimen of the proper mode of heating the air, — we 

 shall see how the heat is diffused, so that the hottest portions 

 become cooled, and the cool heated ; but we shall look in vain 

 for an equality of temperature. Such was not Nature's purpose. 

 An earth unequally heated produced and required for its inha- 

 bitants, both animal and vegetable, an unequally heated atmo- 

 sphere. We shall not find her imparting to her favourites a 

 great amount of bottom heat while the atmospheric temperature 

 is low, thus stimulating a flow of sap which the leaves are un- 

 able to dispose of ; neither shall we find her with high atmo- 

 spheric heat and a low soil temperature, inducing a foliage which 

 the roots cannot afford materials to maintain. These are man's 

 plans, not Nature's. When shall we, by observing her beauti- 

 fully-adjusted balance, learn to regulate our own ? And as a 

 uniformity of atmospheric temperature around our globe would 

 have been an imperfection, we shall look in vain to Nature for 

 the example or the principle of the objects of our search. But 

 is Philosophy equally silent ? Will she point out no way ? She 

 has with Nature pointed to the means, but she is left alone to 

 discover how to use them. It will be observed, that in the mo- 

 tions of the earth's atmosphere towards those portions of the 

 earth that are most highly heated, — in other words, the flow of 

 air from the poles to the equator, the hottest portion of the air 

 is always succeeded by the hottest but one, — that a particle of 

 air, for instance, that leaves the poles would travel onwards by 

 degrees to the equatorial regions, acquiring warmth on its way, 

 till arrived at the equator (presuming no other force interfered 

 to derange its course) ; and while we can easily see in these cur- 

 rents a powerful means of preventing too great a difference in 

 the atmospheric temperature, a means sufficient to secure the end 

 designed, still they are not such as can possibly occasion a uni- 

 formity of heat. Surely common sense would tell us, that if uni- 

 formity is our object, we should take not that portion of air first 

 to the heat which is hottest but one, but that which is coldest of 

 all. Does not philosophy teach us that rapidity of current de- 

 pends mainly on difference of temperature, and that therefore we 

 must not only use the means that can travel the fastest, but we 

 must subject them to the conditions that shall insure their doing 

 so, — such is Polmaise. The air which is taken first to the 



