VOL. LXV.] PHILOSOPHICAL TKANSACTIONS. 60Q 



the thermometers they brought with them into the room, none of which at the 

 end of 20 minutes, in the first experiment, had acquired the real heat of the 

 air by several degrees. It might be supposed, that by an action so very different 

 from that to which the human body is accustomed, as destroying a large quantity 

 of heat, instead of generating it, they must have been greatly disordered. And in- 

 deed they experienced some inconvenience; their hands shook very much, and 

 they felt a considerable degree of languor and debility ; Dr. B. had also a noise 

 and giddiness in his head. But it was only a small part of their bodies that exerted 

 the power of destroying heat with such a violent effort as seems necessary at first 

 sight. Their clothes, contrived to guard them from cold, guarded them from 

 the heat on the same principles. Underneath they were surrounded with an 

 atmosphere of air, cooled on one side to 98°, by being in contact with their 

 bodies, and on the other side heated very slowly ; because woollen is such a bad 

 conductor of heat. Accordingly Dr. B. found, toward the end of the first 

 experiment, that a thermometer put under his clothes, but not in contact with 

 his skin, sunk down to 110°. On this principle it was that the animals, sub- 

 jected by M. Tillet to the interesting experiments related in the Memoirs of the 

 Academy of Sciences for the year 1 764, bore the oven so much better when 

 they were clothed, than when they were put in bare : the heat actually applied to 

 the greatest part of their bodies was considerably less in the first case than in the 

 last. As animals can destroy only a certain quantity of heat in a given time, so the 

 time they can continue the full exertion of this destroying power seems to be 

 also limited ; which may be one reason why we can bear for a certain time, and 

 much longer than can be necessary to fully heat the cuticle, a degree of heat 

 which will at length prove intolerable. Probably both the power of destroying 

 heat, and the time for which it can be exerted, may be increased, like most 

 other faculties of the body, by frequent exercise. It might be partly on this 

 principle that, in M. Tillet's experiments, the girls who had been used to attend 

 the oven bore, for 10 minutes, a heat which would raise Fahrenheit's thermo- 

 meter to 270^ : in the above experiments however, not one of them thought 

 he suffered the greatest degree of heat that he was able to support. 



A principal use of all these facts is, to explode the common theories of the 

 generation of heat in animals. No attrition, no fermentation, or whatever else 

 the mechanical and chemical physicians have devised, can explain a power capable of 

 producing or destroying heat, just as the circumstances of the situation require. 

 A power of such a nature, that it can only be referred to the principle of life 

 itself, and probably exercised only in those parts of our bodies in which life seems 

 peculiarly to reside. From these, with which no considerable portion of the 

 animal body is left unprovided, the generated heat ' may be readily communi- 

 cated to every particle of inanimate matter that enters into our composition. 



VOL. XIII. 4 I 



