34 THE FAUNA OF THE DEEP SEA 



it does not come from the surface. Nor is it at all 

 probable that it comes from the earth upon which 

 the water rests ; for, if it were so, the temperature for 

 water of a given depth would always be the same. 

 We should not find the bottom temperature of 0'4 C. 

 at 2,900 fathoms off Rio de la Plata and a tempera- 

 ture of 2-2 F. in 4,561 fathoms off Porto Rico. 



In fact the only hypothesis that can with any 

 show of reason be put forward to account for the 

 temperature of the bottom of the ocean is that which 

 derives its coldness from the Polar ice. 



We have at present very little evidence to enable 

 us to judge of the force and direction of the polar 

 currents in the two hemispheres, but the researches of 

 the ' Challenger ' prove almost conclusively that in the 

 Atlantic Ocean there is a very strong predominance 

 of the Antarctic polar current. In fact it seems very 

 probable that the Arctic polar current, if it exist at 

 all, is very small and confined to the eastern and 

 western shores of the North Atlantic. 



It is very probable, however, that these cur- 

 rents at the bottom of the ocean are extremely slow, 

 and, as the water is never affected by tides or storms, 

 the general character of the deep sea is probably 

 one of calm repose. This is a matter of no little 



