[ 3^3 ] 



Anu Condamine tells us, that eighty-five feet per fecond is 

 the moft violent florm whofe velocity can be meafured at fea. 

 Mem. Paris, 1757, p- 637, 8vo.- 



Derham and Kraft's obfervations a2;ree with thofe of Smeaton. 

 By means of this table*, if the velocity of wind be known by 

 any inftrument, its force may alfo be difcovered, and vice verfa. 

 The effed of the velocity of wind, inafmuch- as it refpeds eva- 

 poration, Sauffure has deteded, by new and ingenioufly con- 

 trived, though indired experiments, on Col de Geant and aX Geneva, 

 and found that air, moving at the rate of forty feet per fecond, 

 triples 'the quantity of evaporation that would happen in calm 

 air. He has fhewn, that in this cafe alfo, the greater or lefTer fa- 

 turability of the air is a circumftance that materially afteds the 

 magnitude of the efFed» That on plains, a diiference of one 

 degree of faturability is equivalent to a difference of 1 1 ° Fahr. 

 of heat ; and on heights, on which the barometrical height is 

 diminifhed one-third, its influence is equal to that of heat. 



Hence we fee, that the warmer air is, the quicker its motion, 



the greater its faturability, and the longer its duration, the 



more it will promote evaporation. 



Section 



*The beft portable inftrument for meafuring the force of wind is that invented by 

 Dr. Lind, Phil. Tranf. 1775. 



