THEO R T of RAIN. 



43 



THERE are juft three different ratios, in which this operation 

 of heat on water may be conceived as proceeding. 



1. THE folution may vary at the fame rate with the heat, fo 

 that equal increments of heat mall be accompanied by equal in- 

 crements of diffolved vapour. 



2. IT may vary at a greater rate, fo that while the heat in- 

 creafes by equal differences, the quantity of diffolved vapour 

 mall increafe by differences which are continually augmenting. 



3. IT may vary at a lefs rate than the heat, fo that while the 

 heat increafes by equal differences, the quantity of diffolved va- 

 pour mall increafe by differences which are continually dimi- 

 nifhing. 



THESE three rates of 

 evaporation, or folution of 

 water in air, may be re- 

 prefented geometrically, 

 thus : Let the ftraight 

 line C H reprefent the 

 fcale of the thermometer. 

 Let the perpendicular or- 

 dinates, am, b r, be taken in the proportion of the quantity 

 of water, which can be held in folution, by a given quantity of 

 air, of the temperatures a and b. Draw the ftraight line m r. 

 Draw alfo the curve m d e f r, having its convexity turned to- 

 wards C H ; and the curve m v k I r, having its concavity 

 turned towards C H. It is evident, that the ordinates to the 

 line m r will mark the progrefs of heat, and alfo of a folution, 

 varying at the fame rate with the heat. In like manner, the 

 ordinates to the curve m d ef r, will mark the progrefs of fo- 

 lution, varying at a greater rate than the heat ; and the ordi- 

 nates to the curve m g k I r, will mark the progrefs of folution, 

 varying at a lefs rate than the heat : For thefe ordinates are 

 taken in the proportion of the quantity of water diffolved in 



F 2 



air. 



