CHAP. VIT.] DEEP-SEA TEMPERATURES. 317 



continuous with the general basin of the North 

 Atlantic. 



The temperature of this ocean valley was investi- 

 gated with great care during the first and second 

 cruises of the ' Porcupine ' in 1869, and the results 

 were so very uniform throughout the area that it 

 will be needless to describe in detail the slight 

 differences in different localities. These differences, 

 in fact, only affected the surface layer of the water, 

 and depended merely upon differences of latitude. 

 The temperatures in deep water may be said to 

 have been practically the same everywhere. The 

 first chain of soundings, taken by Captain Calver 

 during the first cruise under the scientific direction 

 of Mr. Gwyn Jeffreys, was between Lough Swilly 

 and Rockall. The greatest depth, 1,380 fathoms, is 

 in the middle of the channel, and a sounding at 

 that depth, lat. 56 24' IS"., long. 11 49' W., gave 

 a bottom temperature of 2*S C. A depth of 630 

 fathoms, No. 23, a little to the south of Rockall, 

 gave a temperature of 6*4 C., almost exactly the 

 same as the temperature of a like depth in the warm 

 area off the entrance of the Pseroe Channel ; and a 

 temperature at 500 fathoms, one of a series taken 

 at Station 21 with a bottom temperature at 1,476 

 fathoms of 2'7 C., was 8'5 C., rather less than a 

 degree higher than the temperature at a correspond- 

 ing depth at Station 87. At Station 21 the tempera- 

 ture was taken at every 250 fathoms. 



Surface 13*5C. 



250 fathoms 9*0 



500 8-5 



750 5 8 



