CHAP. VII.] DEEP-SEA TEMPERATURES. 325 



perature for the last mile and three-quarters is its 

 absolute uniformity, which appears to be incon- 

 sistent with the idea of anything like a current in 

 the ordinary sense, and rather to point to a slow 

 and general indraught of cold water, falling in 

 chiefly by gravitation from the coldest and deepest 

 sources available, to supply the place of the warm 

 water constantly moving to the northward. 



In 1870, Mr. Gwyn Jeffreys took his first tem- 

 perature observations at the mouth of the Channel, 

 and found them to correspond very closely with 

 those of the previous year ; on the 9th of July the 

 bottom temperature at 358 fathoms. Station 6 PI. V., 

 was 10°-0 C, against 9°'8 C, at about the same depth 

 in a seriarl sounding in 1869, in the immediate 

 neighbourhood. The next few soundings, Stations 

 10 to 13, are in comparatively shallow water, off the 

 coast of Portugal, while the next four Stations, a 

 little north of Lisbon, may serve as an example of 

 the temperatures to a considerable depth in that 

 latitude. Station 14, 469 fathoms, with a surface 

 temperature of 18°'3 C, has a bottom temperature of 

 10°'7 C. ; Station 15, at 722 fathoms, a temperature 

 of 9°-7 C. ; Station 16, at 994 fathoms, 4°-4 C. ; and 

 Station 17, at 1,095 fathoms, 4°-3 C. This result is 

 very similar to that which we met with in 1869 off 

 Usliant. With certain differences, which seem to de- 

 pend mainly upon the differences of latitude, we have 

 the same phenomena: — a thin surface-layer, superheated 

 by the direct rays of the sun ; a layer of warm water 

 through which the temperature descends very slowly 

 down to 800 fathoms ; a zone of intermixture and 

 rapid descent of the thermometer of nearly 200 



