222 GRAVITY, LIGHT, AND CALORIC. L.ECT. XL 



of determining whether there existed any difference in the 

 refrigeration going on in an animal, by its immersion in an 

 atmosphere colder than its own, according as this was 

 moist or dry ; and the conclusion was, that it was the same 

 in both cases. If we consider that in moist air heat ought 

 to be diffused more easily than in dry air, we may explain 

 the result which Edwards obtained, by saying that the re- 

 frigeration produced by the more considerable evaporation 

 which takes place in dry air, can be compensated for by 

 the loss of heat effected by contact with moist air. But 

 there is, on the contrary, a very considerable difference 

 in the cooling of an animal, according as the atmosphere 

 is calm or agitated. When it is tranquil, and at a tempe- 

 rature below that of our own body, we lose heat by evapo- 

 ration, by contact with air, and by radiation. The pre- 

 sence and nature of the gas and its agitation, have no per- 

 ceptible influence on the loss by radiation ; but this is 

 not the case with the loss occasioned by evaporation or 

 by contact with the air, which is considerably augmented 

 by the motion of the air. These results are evidently the 

 consequence of the physical laws of the cooling of bodies 

 in the air, and of the effects of evaporation. Parry re- 

 lates, that he has often supported a temperature of 17-77 

 centig. [=0 Fahr.,] without suffering therefrom, when 

 the atmosphere was calm ; whilst a cold of 6-66 cen- 

 tig. [== 20 Fahr.] was very annoying, when accompanied 

 by even a slight wind. And the surgeon, who accompanied 

 Captain Parry in his celebrated expedition, relates, that in 

 a calm air, the sensation produced by a temperature of 

 46-ll centig. [= 51 Fahr.] might be compared to that 

 which they experienced at 17-77 centig. [= Fahr.] 

 with a breeze. It follows from this observation, that a 

 certain agitation of the air will produce a sensation of cold 



