444 Of the Propagation of Heat 



the Heat, it appears that the warmth of the bodies men- 

 tioned in the foregoing table are as the times of cool- 

 ing, the conducting powers being inversely as those 

 times, as I have formerly shown. 



From the results of the foregoing experiments it ap- 

 pears that, of the seven different substances made use 

 of, hares' fur and eider-down were the warmest ; after 

 these came beavers' fur, raw silk, sheep's-wool, cotton- 

 wool, and, lastly, lint, or the scrapings of fine linen; 

 but I acknowledge that the differences in the warmth of 

 these substances were much less than I expected to have 

 found them. 



Suspecting that this might arise from the volumes or 

 solid contents of the substances being different (though 

 their weights were the same), arising from the difference 

 of their specific gravities ; and as it was not easy to 

 determine the specific gravities of these substances with 

 accuracy, in order to see how far any known difference 

 in the volume or quantity of the same substance, con- 

 fined always in the same space, would add to or diminish 

 the time of cooling, or the apparent warmth of the 

 covering, I made the three following experiments. 



In the first, the bulb of the thermometer was sur- 

 rounded by 1 6 grains of eider-down ; in the second by 

 32 grains; and in the third by 64 grains; and in all 

 these experiments the substance was made to occupy 

 exactly the same space, viz. the whole internal capacity 

 of the glass globe, in the center of which the bulb of 

 the thermometer was placed ; consequently, the thick- 

 ness of the covering of- the thermometer remained the 

 same, while its density was varied in proportion to the 

 numbers i, 2, and 4. 



The results of these experiments were as follows : 



