PHILOSOPHICAL TRANSACTIONS. 



137 



VOL. LXXXII.] 



I introduced successively l6 grains in weight of each of these substances into 



the orlobe of the passage-thermometer, and placing it carefully and equally 



round the bulb of the thermometer, I heated the thermometer in boiling water, 



as before described, and taking it out of the boiling water, plunged it into pounded 



ice and water, and observed the 



„ ,. The bulb of the thermometer surrounded by air. 

 times oi coolmg. 



But as the interstices of these 

 bodies thus placed in the globe 

 were filled with air, I first made 

 the experiment with airalone, and 

 took the result of that experiment, 

 as a standard by which to com- 

 pare all the others ; the results of 

 three experiments with air were 

 as annexed. 



The following table shows the results of the experiments, with the various 

 substances mentioned : 



Now the warmth of a body, or its power to confine heat, being as its power 

 of resisting the passage of heat through it (which I shall call its non-conducting 

 power,) and the time taken up by any body in cooling, which is surrounded by 

 any medium through which the heat is obliged to pass, being, cseteris paribus, 

 as the resistance which the medium opposes to the passage of the heat, it appears 

 that the warmth of the bodies mentioned in the foregoing table are as the times 

 of cooling; the conducting powers being inversely as those times, as I have for- 

 merly shown. 



From the results of the foregoing experiments it appears, 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; cottonwool; 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 exj^ected to have found them. 



VOL. XVII. T 



