16 
MBAS TEXIPEBATUHB. 
tiire of the atmosphere, and the lake receives streams whies 
rise from several cold springs in the neighbouring mountains. 
I have to regret that, notwithstanding its small depth, I could 
not determine the temperature of the water at thirty or 
forty fathoms. I was not provided with the thermometrical 
sounding apparatus which I had used in the Alpine lakes 
of Salzburg, and in the Caribbean Sea. The experiments 
of Saussure prove that, on both sides of the Alps, the lakes 
which are from one hundred and ninety to two hundred and 
seventy-four toises of absolute elevation* have, in the middle 
of winter, at nine hundred, at six hundred, and sometimes 
even at one hundred and fifty feet of depth, a uniform 
temperature from 43 to 6 degrees : but these experiments 
have not yet been repeated in lakes situated under the 
torrid zone. The strata of cold water in Switzerland are 
of an enormous thickness. They have been found so near 
the surface in the lakes of Geneva and Bienne, that the 
decrement oi heat in the water was one centesimal degree 
for ten or fifteen ieet ; that is to say, eight times more rapid 
than in the ocean, and forty-eight times more rapid than in 
the atmosphere. In the temperate zone, where the heat of 
the atmosphere sinks to the freezing point, and far lower, 
the bottom of a lake, even were it not surrounded by glaciers' 
and mountains covered with eternal snow, must contain 
particles of water which, having during winter acquired at 
the surface the maximum of their density, between 3-4° and 
4-4°, have consequently fallen to the greatest depth. Other 
particles, the temperature of which is + 0‘5°, far from 
placing themselves below the stratum at 4°, can only find 
their hydrostatic equilibrium above that stratum. 'Thev 
will descend lower only when their temperature is aug- 
mented 3° or 4° by the contact of strata less cold. If 
water in cooling continued to condense uniformly to the 
freezing point, there would be found, in very deep lakes 
and basins having no communication with each" other (what- 
ever the latitude of the place), a stratum of water, the 
temperature of which would be nearly equal to the maxi- 
mum of refrigeration above the freezing point, which the 
lower regions of the ambient atmosphere annually attain. 
* This is the difference between the absolute elefatious of the lakee of 
Geneva and Thun. 
