43^ Of the Propagatiofi of Heat 



To this end, I began by determining by actual experi- 

 ment the relative conducting powers of various bodies 

 of very different natures, both fluids and solids ; of some 

 of which experiments I have already given an account 

 in the paper above mentioned, which is published in the 

 Transactions of the Royal Society for the year 1786 : 

 I shall now, taking up the matter where I left it, give 

 the continuation of the history of my researches. 



Having discovered that the Torricellian vacuum is a 

 much worse conductor of Heat than common air, and 

 having ascertained the relative conducting powers of air, 

 of water, and of mercury, under different circumstances, 

 I proceeded to examine the conducting powers of vari- 

 ous solid bodies^ and particularly of such substances as 

 are commonly made use of for cloathing. 



The method of making these experiments was as fol- 

 lows : a mercurial thermometer (see Fig. 4), whose 

 bulb was about -^-^^ of an inch in diameter, and its 

 tube about 10 inches in length, was suspended in the 

 axis of a cylindril:al glass tube, about |- of an inch in 

 diameter, ending with a globe i j^q- inch in diameter, in 

 such a manner that the center of the bulb of the ther- 

 mometer occupied the center of the globe ; and the 

 space between the internal surface of the globe and the 

 surface of the bulb of the thermom-eter being filled with 

 the substance whose conducting power was to be de- 

 termined, the instrument was heated in boiling water, 

 and afterwards, being plunged into a freezing mixture of 

 pounded ice and water, the times of cooling were ob- 

 served, and noted down. 



The tube of the thermometer was divided at every 

 tenth degree from 0°, or the point of freezing, to 80°, 

 that of boiling water ; and these divisions being marked 



