TEMPEIUTUliE OF THE SEA. 71 



one being cold, the other hot ; their directions also 

 cross each other in a thousand ways. There may thus 

 be many successive beds or strata of currents, their 

 density in each case being the greater in proportion 

 to the depth from the surface at which they are situ- 

 ated. As a proof that such different currents really 

 exist, it may suffice to mention the suddenness with 

 which the thermometer varies after passing through 

 a certain depth of water, and then continues constant 

 while the plummet descends through a lower bed. 



Thermometric soundings have marked a tempera- 

 ture of 41'' Fahr. in the latitude of 43° and 37° under 

 the equator, at the same depth, of somewhat less than 

 6,000 feet. This agrees with the direction of the sub- 

 marine currents, coming respectively from the poles 

 and from tlie equator. In the torrid zone between 

 33° and 34° Fahr. have been indicated at a depth of 

 12,000 feet, whilst the temperature at the surface was 

 about 80° Fahr. This result will be thought less sur- 

 prising if we bear in mind that while fresh-water 

 attains its maximum density at 39° 5' FaLi., average 

 sea-water does not arrive at its degree of maximum 

 density until it passes its freezing-point (27° 2') and 

 reaches the temperature of 25° 6'. 



As sea-water is not easily penetrated by the rays 

 of the sun, it keeps pretty nearly at the temperature 

 of the locality where it has been detained for any 



