JO ON EVAPORATION^. 



at the fame time the temperature of the water was obferved, 

 the force of the aqueous atmofphere afcertained as above, and 

 the ftrength of the current of air noticed* From a great va- 

 riety of experiments made both in the winter and fummer, 

 and when the evaporating force was ftrong and weak, I have 

 found the refults, entirely conformable with the above theory. 

 The fame quantity is evaporated with the fame evaporating 

 force thus determined, whatever be the temperature of the 

 air, as near as can be judged ; but with the fame evaporating 

 force^ a ftrong wind will double the effedt produced in a ftill 

 atmofphere. Thus, if the aqueous atmofphere be correfpond- 

 ent to 40*^ of temperature and the air be 60°, the evaporation 

 is the fame as if the aqueous atmofphere were at 60° of tem- 

 perature and the air 72* ; and in a calm air the evaporation 

 from a velTel of fix inches in diameter in fuch circumftances 

 would be about .9 of a grain per minute, and about 1.8 grains 

 per minute in a very ftrong wind; the different intermediate 

 quantities being regulated folely by the force of the wind. 

 Account of the The following table exhibits the ratios and quantity of water 

 *at»o^ ^**^°' evaporated in each temperature, derived from the preceding 

 theory, and confirmed by experiments, as far as they have 

 been extended. The firft column exprefles the temperature; 

 the fecond, the correfponding force of vapour taken from the 

 preceding table; the other three columns give the number of 

 grains of water that would be evaporated from a furface of fix 

 inches in diameter in the refpedlive temperatures, on the fup# 

 polition of there being previoufly no aqueous vapour in the at- 

 mofphere. Thefe columns prefent the extremes and the mean 

 of evaporation, likely to be noticed, or nearly fuch: for, the 

 (irft is calculated upon the fuppofition of 3.5 grains lofs per 

 mimite from the veflfel of .3| inches in diameter; the fecond, 

 46 and the third 55 grains per minute. 



TABLE 



