On the Radiation of Cold. 209 



heat, they do so as well at one degree of temperature as at 

 another; and presuming that the heat so radiated must have 

 the same temperature (it" I may be allowed such a mode of 

 expression) as the body trom which it proceeds, it will fol- 

 low, that the piece of ice will radiate heat which cannot 

 have a higher temperature than 32'' at the utmost ; and this 

 will of c-ourse instantly affect the thermometer, and even 

 the hand of a person placed in the focus of the opposite 

 mirror, as Mr. Davy stated that it did his : an effect incon- 

 ceivable upon the idea that merely a small portion of warm 

 air had been removed. 



If a frignrific mixture was put info two vessels, one of 

 which when filled with a heated substance radiated much 

 lieat, and the other the contrary ; and if the thermometer 

 was more depressed by the first being placed in the focus 

 than the second, it mi^ht be considered as a decisive proof 

 of the truth of this explanation, and the radiation of cold 

 as it is called would be fully established : and indeed as no 

 otie now doubts that the only difference between heat and 

 cold is a difference of temperature, and as it is known that 

 one temperature is as readily communicated as the other, 

 there seems no reason to be surprised that a body at sa"* 

 should radiate as well as one at 212°. 



The important consequences that must follow from the 

 establishment of this idea, in explaining many of the phae- 

 nomena of nature, must appear so obvious to every one 

 who has at all considered the subject, that I hope these 

 suggestions may be thought worthy of consideration, as 

 they may be readily either confirmed or refuted by those 

 who have the necessary apparatus and assistance at their 

 command, both of which are wanting to one who can con- 

 sider himself in these matters merely as a looker-on. 



March 1812. Z. Z. 



%* Having the present opportunity, I shall, as others 

 have ventured to do, ofier what I conceive to be the true 

 explanation of the phaenomenon above alluded to. The 

 facility with which radiation of temperature is effected,, de- 

 pends, in some degree, on the temperature of the body on 

 which the radiation falls. If two bodies of equal tempera- 

 ture be placed in the focus of the two reflecting surfaces, it 

 is evident that their radiant powers must be perfectly ba- 

 lanced. But let one ot tlieiTi be of a higher temperature 

 than the other, then the body of lower temperature being 

 in a capacity to receive an increase, it seems obvious that. 



Vol. 39. No. 1G7. March 18 IS?. O being 



