[ ^89 J 



air,, and in fummer a few clee;ree.s lower; hut of tiie variable in- 

 fluences of the winds, or of the fdturability of the air, 1 can give 

 no account, except that of 'his laft 1 may fay, that the hygrometer 

 never flood lower than jo'^ ; but as thefe influences fometimes 

 concurred with, and*fometimes oppofed, the adion of heat, it is 

 probable that, in producing the general eftedt colietled from a num- 

 ber of experiments, they balanced each other. 



2.". With refpe6t to/urface, it is now generally agreed, in con- 

 fequence of the numerous and accurate experiments of Wallcrius 

 and Richman, repeated and confirmed by Lambert, that other 

 circumftances relative to the air and to the water being alike, eva- 

 poration, in equal times^ is exaiStly in the ratio of the extent of 

 the furface which water expofes to the atmofphere ; and hence it 

 is, that agitation of the water, by increafing and varying the fur- 

 faces, promotes evaporation. Yet IVrufchenbrock, in his notes on 

 , the experiments of the Academy a'e/ Cimento, relates fome, in 

 which he found, as he imagined, that the depth of v^^ater coa- 

 curred with the furface in promoting evaporation j fo that if the 

 furfaces were equal, the evaporation would be as the cube-roots 

 of the depths'; thus evaporation, from a veffel eight inches deep, 

 and filled with water, v/ould be twice greater, than the evapora- 

 tion from another veffel of equal furface in the aperture, but 

 only one inch in depth. In this experiment both vefTels were of 



lead, 



