the Weight ascribed to Heat. 13 



and their contents had acquired the exact temperature 

 of the surrounding air, I wiped them very clean, and, 

 comparing them together, I found their weights re- 

 mained unaltered. 



This experiment I afterwards repeated several times, 

 and always with precisely the same result, the water 

 in no instance appearing to gain, or to lose, the least 

 weight upon being frozen or upon being thawed ; 

 neither were the relative weights of the fluids in either 

 of the other bottles in the least changed by the various 

 degrees of heat and of cold to which they were exposed. 



If the bottles were weighed at a time when their con- 



O 



tents were not precisely of the same temperature^ they 

 would frequently appear to have gained, or to have 

 lost, something of their weights ; but this doubtless 

 arose from the vertical currents which they caused in 

 the atmosphere, upon being heated or cooled in it, or 

 to unequal quantities of moisture attached to the sur- 

 faces of the bottles, or to both these causes operating 

 together. 



As I knew that the conducting power of mercury, 

 with respect to heat, was considerably greater than either 

 that of water or that of spirit of wine, while its ca- 

 pacity for receiving heat is much less than that of either 

 of them, I did not think it necessary to inclose a ther- 

 mometer in the bottle C, which contained the mercury ; 

 for it was evident that, when the contents of the other 

 two bottles should appear, by their thermometers, to 

 have arrived at the temperature of the medium in which 

 they were exposed, the contents of the bottle C could 

 not fail to have acquired it also, and even to have ar- 

 rived at it before them ; for the time taken up in the 

 heating or in the cooling of any body, is, c<eteris paribus. 



