155 



) 



temperature of the air ; either from the effect of 

 evaporation *, which carries off caloric from 

 the air and the water ; or because a great mass 

 of water does not follow with an equal rapidity 

 the changes of temperature of the atmosphere, 

 and the lake receives streams, that rise from 

 several cold springs in the neighbouring moun- 

 tains. I have to regret, that, notwithstanding 

 it's small depth, I could not determine the 

 temperature of the water at thirty or forty 

 fathoms. I was not provided with the thermo- 

 metrical sounding apparatus, which I had used 

 in the Alpine lakes of Saltzburg -f, and in the 

 Caribbean sea. The experiments of Saussure 

 prove, that, on both sides of the Alps, the lakes 

 that are from one hundred and ninety to two 

 hundred and seventy-four toises of absolute 



* 



* We shall see hereafter, that, according to observations 

 made at Cumana on the produce of evaporation, the temper- 

 attire of the water in vessels exposed to the Sun during seven 

 or eight hours constantly remained, at the end of the experi- 

 ment, from 1° to 1 '8° below the temperature of the air in the 

 shade. 



+ See above, vol. i, p. 38. I made the following obser- 

 vation, on the 16th of April, 1798, at four in the afternoon, 

 on the lake of St. Bartholomew, in the Alps of Berchtes- 

 gaden, behind Falkenstein. Air, at the shore, therm. 17*7° 

 cent. ; hair-hygrometer 56°. Air at the centre of the lake, 

 th. 16° ; hyg. 68°. Water of the lake, at a depth of two 

 feet, th. 7 7° at fortv-two feet, th. 6*2° ; at sixty feet, th. 

 5° j and in another place, at eighty-four feet, therm. 5*6<\ 



