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Wallerius alfo found, that ice evaporates in proportion to its. 

 furface and temperature, though lefs than water equally cold ; and 

 that it evaporates more during congelation than when its conge- 

 lation is completed. And hence it is, that ice and water evaporate 

 more than mere water of the fame temperature, and fo much the 

 more as the air is colder, probably becaufe congelation is pro- 

 moted by air in proportion as the air is colder; nay, evaporation 

 is checked during a thaw. 1 1 Colled Acad. 263, &c.- 



The evaporation of ice was denied by Baron, but it was afcer- 

 tained beyond all poffibility of doubt by the accurate experiments 

 of Sauffure. Hygrom § 130. Baron however has proved, that 

 ice expofed to wind lofes confiderably by abrafion, the wind car- 

 rying off its particles in an exceeding fine powder. Sauffure alfo 

 obferved, that ice evaporates in air four or five degrees colder than 

 itfelf. 



TviY.Jiate of the air in contadl with water comes next under our 

 confideration, as it materially affedts the quantity of evaporation. 

 Air may be confidered either with refped to its denfity, or with 

 refped to its temperature, or with that of its affinity, which again 

 involves the confideration of denfity, or with regard to its agitation, 

 or with regard to its eleBricity. 



And, 



V 



