•VOL. LXXVIl.] PHILOSOPHICAL TRANSACTIONS. 289 



the heat. Dr. Cnllen ascribed this power to a peculiar quality in animals dif- 

 ferent from the powers of inanimate matter. We saw a confirmation of this 

 power being very great when we kept a dog of no large size (he might weigh 

 about 25 lb.) in air heated to ]6o degrees of Fahrenheit's thermometer for half 

 an hour. We took him out with only the addition of a few degrees of heat; 

 not from any uneasiness of the animal, but from being satisfied with the experi- 

 ment. This power has been shown by Mr. Hunter to extend to vegetables. 

 The degree of heat one body is capable of impregnating another with, was 

 hardly touched on by any author before Dr. Crawford, who has done a great deal 

 in this branch, and is still pursuing it. 



The subject of the present inquiry is different from all these. The proposi- 

 tion is, supposing we can make an applipation to a cold body, so as to produce 

 heat in it, and this application be made with the same force to the same body, 

 whether by this means an equal quantity of heat will always be produced in an 

 equal quantity of matter? That is, for instance, whether an equal quantity of 

 the rays of the sun being thrown on an equal surface of the same matter, so 

 that they shall be equally lost, bent, or reflected, an equal mass of matter below 

 shall be equally heated according to its capacity; whether equal vibrations excited 

 shall always produce the same quantity of heat; whether a chemical attraction 

 taking place between an equal quantity of two substances shall always produce an 

 equal quantity of heat? 



The importance of this inquiry is sufficiently evident, since, if the same quan- 

 tity of fuel being burnt, the same quantity of heat be always produced, our whole 

 attention will be to take care that no part of the heat shall be lost; but if burn- 

 ing the fuel under one set of circumstances will actually produce a greater quan- 

 tity of heat than burning it in other circumstances; or if burning it, will pro- 

 duce a great heat in one place, which cannot be carried to another place, but 

 will be again annihilated, a very different attention must be paid. I was first led 

 into this train of thinking by observing reverberatory furnaces. Formerly I had 

 no doubt but that it was obvious, that the same quantity of fuel burnt would 

 produce the same quantity of heat; but having occasion to try some experiments 

 in reverberatory furnaces, where great heat and cleanness were required, I tried 

 to heat the furnace with charcoal and coak, or pit-coal charred, that is, burnt 

 till no smoke arises, but could never produce the heat required, though I could 

 do it easily with coal. I insulated my furnace, so that after 24 hours strongest 

 fire, it did not feel in the least warm on the outside. I heightened the chimney; 

 but all to no effect: in the fire-place the heat was sufficient to melt malleable iron, 

 but in the laboratory, in the horizontal part of the chimney, the heat was triflings 

 Since that time I have made various experiments to ascertain the proposition laid 

 down. The following one, which has been varied and repeated with the same 

 result, may perhaps draw the attention of chemists to this point. 



VOL. XVi. P P 



