POLMAISE METHOD OF HEATING HOTHOUSES. 



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them ; and such was the position of affairs when I entered on the 

 discussion. My fondness for horticulture urged me to an in- 

 vestigation, for which my acquaintance with the laws regulating 

 the diffusion of heat seemed to fit me. I soon saw that the 

 success of this mode of heating was independent of any peculiar 

 detail as to form of stove, &c. &c, but resulted from the em- 

 ployment or introduction of a novel principle in artificial heat- 

 ing ; this principle being the power the air possesses of acquiring 

 and rapidly distributing heat under certain conditions by its own 

 motion, thus rendering any other means of distribution unne- 

 cessary. And I propose to prove the truth of this principle in 

 various ways, to point out the manner in which it may be con- 

 veniently reduced to practice, and the advantages likely to result 

 from its employment. 



We inhabit a globe surrounded by an atmosphere extending 

 perpendicularly about forty-five miles from the earth's surface ; 

 this atmosphere varies considerably in its temperature, being 

 exceedingly heated in certain localities at certain times ; and 

 as effects do not occur without means, we naturally inquire 

 what are the means Nature employs to produce atmospheric 

 heat. Does the sun heat the air as its rays of heat pass through 

 the air to the earth? Certainly not, for we find that the higher 

 we ascend, and the nearer we approach the sun, the colder the 

 air becomes ; experience also tells us that luminous, radiant 

 caloric has little effect on transparent bodies, whether solid, 

 liquid, or gaseous, passing through them unabsorbed ; therefore 

 the air is not heated by the radiant caloric of the sun. Air 

 cannot be heated by radiation, but only by contact ; but does it 

 touch the source of heat ? Certainly not. Do heated surfaces 

 pass down into it in the form of flues ? or do pipes of hot water 

 (without which some say it is impossible to warm the air nicely) 

 run through its extent ? None of these indispensables exist, and 

 yet the atmosphere is warmed. The radiant caloric passing 

 from the sun through the air becomes absorbed by the earth's 

 surface, the earth is heated, and the atmosphere becomes heated 

 by contact with the earth, Nature's principle clearly being a 

 radiating body and an absorbing body, with which the air is in 

 contact ; so far she instructs us as to the right mode of attempt- 

 ing to heat air, not directly by radiation, for it cannot be done, 

 but by contact with a body which has obtained its heat in that 

 manner. By examining more closely, we shall find Nature 

 instructs us as to the # distribution of the atmospheric heat so 

 acquired. Not only does the sun heat the earth by radiation, 

 but it heats it unequally, because, as different portions of the 

 earth's surface are differently situated with respect to the sun, 

 and as radiant caloric also diminishes in effect as the squares of 



