84 ESSAYS AND OBSERVATIONS 



when it becomes vapour, is expanded tp 

 a bulk 14,000 times greater than when 

 cold ; and to account for evaporation in 

 the ordinary heat of our atmofphere. he 

 takes for granted a doubtful propoQtion, 

 'viz. that the degree of expanlioa is ilrict- 

 ly proportioned to the degree of heat ; 

 from which propofition he calculates as 

 follows : In Sir Ifaac Newton's fcale of 

 heat, the heat of boiling water is 34, the 

 mean heat of Summer is 5, the mean 

 heat of Spring and Autumn 3, and the 

 mean heat of Winter 2. Therefore, if 

 the expanfion of water by 34 degrees of 

 heat be 14,000, the expanlion by 5 de- 

 grees will 2,058, by 3 degrees i,23j:, and 

 by 2, being ihe mean heat of winter, 823, 

 ■which is fufficient to raile water, the den- 

 iaty of which, in its ordinary date, is to 

 that of air as 800 to one. 



But, with the Dolor's leave, here is 

 ^ calculation not a little abfurd; for if, 

 even by winter-heat, water be fb expand' 

 ed as to- be fpecifically lighter than air, 

 by what reftraining power does it remain 

 below, contrary to the power of gravity? 



The 



