38 Temperature of the Ocean. 



This cold area may be traced southwards into the Antarctic 

 region, and northwards as far as the Equator; for at Station 

 112, off Cape St. Roque, the temperature at a depth of 2200 

 fathoms is only o°.5 C, and at Station 110, under the Equator, 

 o°.o C. at a depth of 2275 fathoms. At the two latter stations, 

 the temperature of 5 C. is reached at a depth of little over 300 

 fathoms. 



As early as 1859, the officers of the U.S. Coast Survey found 

 a temperature of 4^4 C. (40 F.) at a depth of 300 fathoms in 

 the Strait of Florida; the water of the Gulf Stream at the 

 surface having, at the same date, a temperature of 2 6°. 7 C, 

 or 8o° F. 



The two principal exceptions to the above-stated rule of the 

 gradual decrease of temperature from the surface towards the 

 bottom are to be found, one in a number of small basins which 

 are cut off by submarine ridges or elevations from communica- 

 tion with the lower strata of the ocean outside, the other in the 

 Arctic and Antarctic regions, where the rule seems to be com- 

 pletely inverted, the temperature of the water increasing from 

 the surface towards the bottom. 



The operations of H.M.S. "Porcupine" in the summer of 

 1870 in the Mediterranean, and the cruise of H.M.S. " Chal- 

 lenger," furnish examples of the first-mentioned exception. It 

 is well known that the Mediterranean Sea is cut off from the 

 depths of the North Atlantic Ocean by a submarine elevation 

 extending from Cape Spartel in Africa to Cape Trafalgar in 

 Spain, and rising to within 100 fathoms from the sea-surface. 

 From a series of temperature-soundings obtained by H.M.S. 

 " Porcupine " at seven different stations between the meridian of 

 Malaga and Carthagena, it appears that the temperature of that 

 part of the Mediterranean falls from a mean of 2 2°.6 C. at the 

 surface to 13 C. at a depth of 100 fathoms, whence it remains 

 stationary at the latter temperature down to the bottom, at 



