[ 3" ] 



Thus Sauffure found the complement of 9,5 to be 3,8739 

 grains, and the quantity at XL. to be 0,8971 of a grain, and 

 by the ratio here given it is 0,8952 of the complement.* 



Section IH. 



Of the Itifluence of Wind. 



The third agent concerned in producing evaporation is z^\i2L~ 

 tion ; whether of water in quiefcent air, or of air itfelf, that is 

 wind, which neceffarily ^'produces the agitation of the water ex- 

 pofed to it. It is evident that the agitation of water promotes 

 evaporation by augmenting its furface to a degree that efcapes 

 calculation. The agitation of air, befides involving that efFcd, 

 promotes evaporation by the rapid removal of vapours as fall as 

 they are formed, and by inceffantly prefenting new furfaces of 

 lefs faturated air, and cooling the water if it be warmer than the 

 air, in which cafe we have already noted the evaporation to be 

 confiderable, or, if both be of the fame temperature, by lower- 

 ing that of the water, or if the air be confiderably warmer than 

 the water, by lowering the difference, and confequently promoting 

 evaporation, as already fhewn. Moft of thefe effeds of wind 

 are proportioned to its faturability, of which enough has been 

 already faid, and to its velocity, of which I fhall now tpjat. 



O^q 2 Mr. 



* How obfervations fliould be made on this inftrument may be feeii in the Appen- 

 dix, Sauflure, 309. 



