Sir Benjamin Thompson's Experiments , & c . 40 
The route which I have followed in this inquiry is that which 
I thought bid fairest to lead to useful discoveries. Without em- 
barrassing myself with any particular theory, I have formed to 
myself a plan of experimental investigation, which I conceived 
would conduct me to the knowledge of certain facts, of which 
we are now ignorant, or very imperfectly informed, and with 
which it is of consequence that we should be made acquainted. 
The first great object which I had in view in this inquiry 
was to ascertain, if possible, the cause of the warmth of certain 
bodies ; or the circumstances upon which their power of con- 
fining heat depends. This, in other words, is no other than to 
determine the cause of the conducting and non-conducting 
power of bodies. 
To this end I began by determining by actual experiment 
the relative conducting powers of various bodies of very diffe- 
rent natures, both fluids and solids, of some of which experi- 
ments I have already given an account in the Paper above men- 
tioned, 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 you 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 ascer- 
tained the relative conducting powers of air, of water, and of 
mercury, under different circumstances, I proceeded to examine 
the conducting powers of various solid bodies, and particularly 
of such substances as are commonly made use of for clothing. 
The method of making these experiments was as follows : a 
mercurial thermometer *, whose bulb was about of an inch 
* See Phil. Trans. Vol. LXXVI. Tab. VI. Fig. 4 
MDCCXCII. H 
