DEEP-SEA BOTTOM TEMPERATURES. 19 



Their existence is also passed, not only in a region 

 of probable perpetual darkness, but also in one certainly 

 of very great permanent cold: the temperature of the 

 water there never rising much above the freezing point 

 of fresh water on the upper earth. Again quoting 

 from the Report of the Challenger Expedition we find 

 that " the normal temperature of this region is from 

 32 to 40 Fahr." * 



With respect to this important point as to the temper- 

 ature of the great deeps, the Encyclopedia Britannic a 

 makes the following observations: 



" Even in the equatorial parts of the Atlantic and Paci- 

 fic oceans, though the upper layers of the water partake in 

 the heat of the intertropical latitudes, a temperature of 40 

 is found within 300 fathoms of the surface; while at the 

 bottom, at depths of 2500 or 3000 fathoms, the temperature 

 (32.4 to 33 Fahr.) is very little above that of the freezing 

 point of fresh water. It has been proved that the bottom 

 temperature of every ocean in free communication with the 

 poles, has a temperature little different from that of the water 

 in polar latitudes. Between Scotland and the Faroe Islands 

 a sounding was obtained giving a temperature of 29.6 or 

 2.4 below the freezing point of fresh water. These ob- 

 servations warrant the conclusion, that a vast system of 

 circulation takes place in the ocean. The heavy, cold, polar 

 water creeps slowly towards the equator, under the upper, 

 lighter water, which moves away towards the poles." f 



Perhaps it is hardly necessary to remind the reader 

 of the well-known facts that both with respect to air 

 and water, a cold current is always heavier than a 

 heated one, and also that " 28 Fahr. is the temperature 

 average sea water invariably assumes during the process 



* Report of H.M.S. Challenger's Expedition, 1880, Vol. i., p. 48. 

 f Encycl. Brit., Qth edit., 1877, Vol. x., p. 211 (Art. "Geography"). 



