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du(^ion lafts, and hence the evaporation from fuch water is often 

 greater at firft than afterwards. 



The moft ftriking proof, and the happieft application of the efE- 

 cacy of multiplied furfaces in promoting evaporation, niay be feen 

 in what are called the houfes of graduation, where waters, con- 

 taining only one per cent, of common fait, are fo far evaporated 

 by the mere multiplication of furfaces, that the refidue contains 

 twenty per cent, and in this ftate, and not before, they are ex- 

 pofed to heat. Such houfes are common in Germany and Swit- 

 zerland. See Haller's account of the procefs in the Paris Me- 

 moirs for 1764. 



The third circumftance relative to the ftate of water, arid which 

 affeds its evaporation, is its /wr/'/fy. It is well known, that con- 

 centrated folutions of moft falts evaporate much more flowly than 

 pure water, in the fame circumftances; but Wallerius has fhewn, 

 that the evaporation from a folution of common fait, whofe fpecific 

 gravity was 1,0466, and confequently containing fixteen per cent, 

 was nearly equal to that of fimple water, after the fait was fully 

 diffolved; but during its folution evaporation is diminifhed by 

 reafon of the cold produced. 



Hence we fee, that under equal furfaces, evaporation from the 

 fea is as confiderable as that from lakes. 

 Vol. VIII. O o Wallerius 



