43$ Of the Propagation 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 y 5 ^ of an inch in diameter, and its 

 tube about 10 inches in length, was suspended in the 

 axis of a cylindrical glass tube, about f of an inch in 

 diameter, ending with a globe \fa 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 thermometer 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 o, or the point of freezing, to 80, 

 that of boiling water ; and these divisions being marked 



