388 ' An Inquiry concerning the Weight 



latice ; when I had the pleafure to find the three thermometers,— wz. that in the bottle 

 A, (which was now inclofedin.afolid cake ofice,) that in the bottle B, and that fuf- 

 pended in the open air of the room, all (landing at the fame point, 29° F, and the bot- 

 tles A and B remaining in (he mojl perJeEl equilibrium. 



To affure myfelf that the play of the balance was free, I now approached it 

 very gently, and caufed it to vibrate; and I had thefatisfaftion to find, not only that it 

 moved with the utmoft freedom, but alfo, when its vibration ceafed, that it relied pre- 

 cifely at the point from which it had fet out. 



1 now removed the bottle B from the balance, and put the bottle C in its place ; and 

 I found that that likewife remained of the fame apparent weight as at the beginning of 

 the experiment, being in the fame perfeft equilibrium with the bottle A as at firft. 



I afterwards removed the whole apparatus into a warm room, and, caufing the ice in 

 the bottle A to thaw, and fuffering the three bottles to remain till they and their contents 

 had acquired the exaft temperature of the furrounding air, I wiped them very clean, 

 and, comparing them together, I found their weights remained unaltered. 



This experiment I afterwards repeated feverai times, and always with precifely the 

 fame refult ; the water, in no injlance, appearing to gain, or to lofe, the leafl weight, 

 upon being frozen, or upon being thawed ; neither were the relative weights of the 

 fluids in either of the other bottles in the leaft changed, by the various degrees of heat, 

 and of cold, to which they were expofed. 



If the bottles were weighed at a time when their contents v;ere not precifely of the fame 

 temperature, thev would frequently appear to have gained, or to have loll, foniething 

 of their weio^hts : but this doubtlefs arofe from the vertical currents which they caui'ed in 

 the atmofphere, upon being, heated or cooled in it : dr to unequal quantities of nioif- 

 tyre attached to the furfaces of the bottles ; — or to both thefe caufes operating together. 



As I knew that the conducing power of mercury, with refpeft to heat, was confidera- 

 bly greater than either that of water, or that of fpirit of wine, while its capacity for re- 

 ceivinff heat is much lefs than that of either of them, I did not think it necelTary to in- 

 clofe a thermometer in the bottle C, which contained the mercury ; for it was evident, 

 that when the contents of the other two bottles Ihould appear, by their thermometers, to 

 have arrived at the temperature of the medium in which they were expofed, the contents 

 of the bottle C could not fail to have squired it alfo, and even to have arrived at it be- 

 fore them ; for, the time taken up in the heating or in the cooling of any body, is, caleris 

 paribus, as the capacity of the body to receive and retain heat, dire&ly, and as its con- 

 dufting power, inverfdy. 



The bottles were fufpended to the balance by filver wires, about two inches long, with 

 hooks at the ends of them; and, in removing and changing the bottles, I took care not 



to 



