in various Substances. 



433 



The total times of heating from o° to 70° in the three 

 experiments with mercury being 41 seconds, 31 seconds, 

 and 48 seconds, the mean of these times is 40 seconds ; 

 and as in the experiment with water the time employed 

 in acquiring the same degree of Heat was \' 57'' = 117 

 seconds, it appears from these experiments that the con- 

 ducting power of mercury to that of water, under the 

 circumstances described, is as 36I to 117 inversely, or as 

 1000 to 342. And hence it is plain, why mercury ap- 

 pears so much hotter, and so much colder, to the touch 

 than water, when in fact it is of the same temperature : 

 for the force or violence of the sensation of what ap- 

 pears hot or cold depends not entirely upon the temper- 

 ature of the body exciting in us those sensations, or 

 upon the degree of Heat it actually possesses, but 

 upon the quantity of Heat it is capable of communicat- 

 ing to us, or receiving from us, in any given short 

 period of time, or as the intensity of the communica- 



