in various Substances. 463 



the Heat communicated to them by the animal body, 

 the air in the fur, though heated, is not easily displaced; 

 and this coat of confined air is the real barrier which de- 

 fends the animal body from the external cold. This air 

 cannot carry off t\\Q. Heat of the animal, because it is it- 

 self confined, by its attraction to the hair or fur ; and it 

 transmits it with great difficulty, if it transmits at all, 

 as has been abundantly shown by the foregoing experi- 

 ments. 



Hence it appears why those furs which are the finest, 

 longest, and thickest, are likewise the warmest ; and how 

 the furs of the beaver, of the otter, and of other like 

 quadrupeds which live much in water, and the feathers of 

 water- fowls, are able to confine the Heat of those ani- 

 mals in winter, notwithstanding the extreme coldness 

 and great conducting power of the water in which they 

 swim. The attraction between these substances and 

 the air which occupies their interstices is so great that 

 this air is not dislodged even by the contact of water, 

 but, remaining in its place, it defends the body of the 

 animal at the same time from being wet, and from being 

 robbed of its Heat by the surrounding cold fluid, and 

 it is possible that the pressure of this fluid upon the 

 covering of air confined in the interstices of the fur, or 

 feathers, may at the same time increase its warmth, or 

 non-conducting power, in such a manner that the ani- 

 mal may not, in fact, lose more heat when in water than 

 when in air: for we have seen, by the foregoing experi- 

 ments, that, under certain circumstances, the warmth of 

 a covering is increased by bringing its component parts 

 nearer together, or by increasing its density even at the 

 expense of its thickness. But this point will be further 

 investigated hereafter. 



