DEEP-SEA TEMPERATURES 27 



recorded the following temperatures : at the surface 

 1 C. ; at 100 m. ri C. ; at 400 m. r6 C. ; at 

 1,000-1,500 m. r6 C. ; at 4,700 m. 0*5 C. These 

 may be compared with some records made in the 

 Sargasso Sea by the Plankton Expedition in the 

 month of August, when the surface registered a tem- 

 perature of 24 C. ; 195 m. one of 18*8 C. ; 390 m. one 

 of 14*9 C. ; and 2,060 m. one of 3*8 C. It is thus clear 

 that the temperature at the bottom of the deep sea 

 varies but a few degrees from the freezing-point ; and, 

 whether in the tropics or around the poles, this tem- 

 perature does not undergo anything like the variations 

 to which the surface of the earth is subjected. 



There are, however, some exceptions to this state- 

 ment. The Mediterranean, peculiar in many respects, 

 is also peculiar as to its bottom temperature. In 

 August, 1 88 1, the temperature, as taken by the 

 Washington, was at the surface 26 C. ; at 100 m. 

 14-5 C. ; at 500 m. 14-1 C. ; and from 2,500 m. to 

 3,550 m. 13-3 C. These observations agree, within one- 

 fifth of a degree, with those recorded later by Chun in 

 the same waters. There are also certain areas near 

 the Sulu Islands where, with a surface temperature 

 of 28 C., the deep sea, from 730 m. to 4,660 m., shows 

 a constant temperature of 10*3 C. ; and again, on the 

 westerly side of Sumatra, the water, from 900 m. 

 downwards, shows a constant temperature of 5-9 C. ; 

 whilst in the not far distant Indian Ocean it sinks at 

 1,300 m. to 4 C, and at 1,700 m. to 3 C. In spite ot 

 these exceptions, we may roughly say that all deep-sea 

 animals live at an even temperature, which differs by 

 but a few degrees from the freezing-point. Indeed, 

 the heating effect of the sun's rays is said not to pene- 

 trate, as a rule, further than 90 to 100 fathoms, though 

 in the neighbourhood of the Sargasso Sea it undoubt- 

 edly affects somewhat deeper layers. In the Mediter- 

 ranean the heat-rays probably do not penetrate more 



