DEEP-SEA TEMPERATURES 27 



recorded the following temperatures : at the surface 

 — I" C. ; at 100 m. — ri" C. ; at 400 m. v6° C. ; at 

 1,000-1,500 m. 1-6° C. ; at 4,700 m. -o'S" 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 i8-8° 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. 

 i4'5° C. ; at 500 m. 14-1° C. ; and from 2,500 m. to 

 3,550 m. 1 3 '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 io'3° C. ; and again, on the 

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

 downwards, shows a constant temperature of S'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 



