^ of WA 'TE R by HE A T. 4C5 



tends to increafe this tenacity, muft, in the fame proportion, 

 augment this want of fenfibility. 



To afcertain whether any fenfible change in the tenacity or 

 fluidity accompanies the expanfion of water by cold, which the 

 theory requires, I examined the mobility of the inftrument 

 when immerfed in water at different temperatures. 1 firft plun- 

 ged it into this fluid, heated to between 60° and 70°. Under 

 due loading, which funk it to the mark on the fl:em, it was not 

 fenfible to a weight lefs than two or three twentieths of a grain. 



I THEN tried it in ice-cold water, and found that its fenfibility 

 was in no perceptible degree impaired. The coldnefs of the 

 water, it muft be remembered, caufes fome degree of contrac- 

 tion of the gravimeter. This contradlion cannot fail to render 

 the inflirument in fome fmall meafure more fenfible, and, fo far 

 as it goes, to counteradl the fluggifhnefs produced by any increa- 

 fed tenacity in the fluid. 



But as the body of the inftrument is made of glafs, the- 

 amount of the contraction muft be very fmall, and the change 

 of fenfibility arifing from it fo very trifling, as certainly by no 

 means to obfcure fuch an effecSl as an increafe of tenacity would 

 occafion. I therefore with fome confidence conclude, that the 

 fluidity of the water is not fenfibly diminifhed, and confequently 

 that the polarity has not begun to exert any fenfible influence \ 

 it can fcarcely, therefore, be accounted the caufe of the dilata^ 

 tion. 



t-NB OF PART SECOND. 



