202 PHILOSOPHICAL TRANSACTIONS. [aNNO 1792. 



phenomenon of the heat rising, and falhng, and rising again, in the bath, with 

 the body at rest, and the teniperature of the surrounding medium unchanged, 

 is I think fatal to those theories of animation which consider the living body 

 as a mere machine, acted on by external powers, but not itself originating action, 

 and differing from other machines only in the peculiarity of the powers which are 

 fitted to set it in motion. I have said that the temperature of the medium con- 

 tinued unchanged, but it may be supposed that the bath was heated a little 

 during the experiments; it was so; but being exposed, with a large surface, to 

 the open air, the wind blowing briskly over it, its heat was little altered; in 12™ 

 immersion it had gained nearly 1°, and 45"", the longest duration of any of the 

 experiments, it liad gained 3°. As this accession was regular, if it had been 

 greater it would not have invalidated the foregoing observations. 



The experiments already recited, suggested the notion, that in all changes 

 from one medium to another of different density, though of the same tempera- 

 ture, there is a loss of animal heat. I found however that this conclusion re- 

 quires many restrictions, l . My experiments being made on bodies of such very 

 different density as air and water, do not admit a universal inference of this sort. 



2. Being all made in a temperature 50° under the human heat, no certain con- 

 clusion can be drawn as to what might happen in degrees of heat much higher, 

 where it is probable the effects of the change, if it appeared at all, might be less 

 striking. It would seem however, that after a person is long chilled in cold 

 water, the first effect of passing through the external air into the warm bath, is 

 first a fall of heat in the air, and after this a still greater fall in the warm bath, fol- 

 lowed however by a speedy rise. 



The air and the water being equally cold, and both 43° or under, I found the 

 loss of heat in passing from the one to the other to be regulated in the following 

 way. 1. If instead of being exposed naked to the wind previous to immersion 

 in the water, the body was kept warm by a flannel covering, the mercury fell much 

 less on the first plunge. 2. If, after plunging into the water, the person con- 

 tinued in it only a minute or 2, a subsequent fall of the mercury did not always 

 take place, on his emerging into the air. On the contrary, there was sometimes a 

 rise on such occasions in the mercury, especially if the atmosphere was at rest. 



3. In one instance, after continuing in the water 15*", on rising into the air in a 

 perfect calm, though during a frost, there was little or no seeming diminution of 

 the heat; while exposure under similar circumstances, with a north-east wind 

 blowing sharply, though the air was many degrees warmer, produced a rapid di- 

 minution. The effects of the wind in diminishing the human heat are indeed 

 striking, and are not in my opinion explained by the common suppositions. 4. The 

 loss of heat by a change of media, depends much on the rapidity of the change. 



