Chap. 4.3 Modes of rendering Sail Water fre/h. 479 



perature of the lake of Geneva, and of other lakes in 

 Switzerland, at different depths ; we learn from them, 

 that in winter time there is very little difference be- 

 tween the heat of the water at the furface, and at a 

 great depth below it ; but that in fummer, the fuper- 

 ficial water is confiderably warmer than that which is 

 at a great diftance from the furface. The experi- 

 ments were made with a thermometer graduated after 

 Reaumur's fcaie; fome of them, reduced to Fahren- 

 heit's fcale, arc expreffed below. 



1 Temperature of the lake of Geneva at different 

 depths, in the beginning of February 1779, after a 

 month's uninterrupted froft. 



' Heat of the open air variable from 37 to 40 de- 

 grees. 



' Water at the furface of the lake - 42^- 

 Depth 100 feet 42^- 



Depth 250 feet 42-i. 



Depth 950 feet, bottom 4^4- 



c In another part of the lake, open air from 37 to 

 40. 



Surface - - 42| 



Depth 350 feet - - 42^- 



Depth 620 feet, bottom 4* -,4- 



c Temperature of the lake of Neuchatel, July 17, 

 1779. 



Air ... 75 .L 



Surface - - 73*.. 



Depth 225 feetj bottom 41*.' 



Sea water may be rendered frem by freezing, which 

 excludes or precipitates the-faline particles, or by dif- 

 tillation, which leaves the fait in a mafs at the bottom 



* Watfon's Chemical Effays, vol. ii. p. 129. 



of 



