442 Of the Propagation of Heat 



was a large earthen jar, being first quite filled with 

 pounded ice, and the water being afterwards poured 

 upon it, and fresh quantities of pounded ice being 

 added as the occasion required. 



Having described the apparatus made use of in these 

 experiments, and the manner of performing the different 

 operations, I shall now proceed to give an account of 

 the experiments themselves. 



My first attempt was to discover the relative conduct- 

 ing powers of such substances as are commonly made 

 use of for cloathing ; accordingly, having procured a 

 quantity of raw silk^ as spun by the worm, sheef s-wool^ 

 cotton-wool, linen in the form of the finest lint, being the 

 scrapings of very fine Irish linen, the finest part of 

 the fur of the beaver separated from the skin, and from 

 the long hair, the finest part of the /^/r of a white Russian 

 hare, and eider-down, — I introduced successively i6 

 grains in weight of each of these substances into the 

 globe of the passage-thermometer, and placing it care- 

 fully and equally round the bulb of the thermometer, I 

 heated the thermometer in boiling water, as before de- 

 scribed, and taking it out of the boiling water, plunged 

 it into pounded ice and water, and observed the times 

 of cooling. 



But as the interstices of these bodies thus placed in 

 the globe were filled with air, I first made the experi- 

 ment with air alone, and took the result of that experi- 

 ment as a standard by which to compare all the others ; 

 the results of three experiments with air were as fol- 

 lows : — 



