( 



157 



find their hydrostatic equilibrium above that 

 stratum. They will descend lower only when 

 their temperature is augmented 3° or 4°, by the 

 contact of strata less cold. If water in cooling 

 continued to condense itself uniformly to the 

 freezing point, there would be found in very 

 deep lakes, and basins of water that have no 

 communication with each other, whatever were 

 the latitude of the place, a stratum of water, 

 the temperature of which would be nearly equal 

 to the maximum of refrigeration above the 

 freezing point, which the lower regions of the 

 ambient atmosphere annually attain. From this 

 consideration it is probable, that, in the plains 

 of the torrid zone, or in the valleys but little 

 elevated, the mean heat of which is from 25*5° 

 to 27°, the temperature of the bottom of the 

 lakes can never be below 21° or 22°. If in the 

 same zone the ocean contain, at depths of seven 

 or eight hundred fathoms, waters the tempera- 

 ture of which is at 7°, that is to say twelve or 

 thirteen degrees colder than the maximum of 

 the heat * of the equinoctial atmosphere over 

 the sea, I think it must be considered as a direct 



* It is almost superfluous to observe, that I am considering 

 here only that part of the atmosphere lying on the ocean be- 

 tween 10° of North and 10° of South latitude. Toward the 

 northern limits of the torrid zone, in the latitude of 23°,wbither 

 the North winds bring with an extreme rapidity the cold air of 

 Canada, the thermometer falls at sea as low as 16°, and even 

 lower. 



