CHAP, v.] THE GULF-STREAM. 363 



west prevented our dredging. At about 1 a.m. there was a 

 sudden rise of the thermometer at the sea surface from 12°-2 C. 

 to 18°-2 C, and it rose steadily during the next eight hours up 

 to 22° C, showing that we had entered the Gulf-stream current. 

 The passage from the dull-green color of the arctic reflux to the 

 deep blue of the Gulf-stream was very perceptible on this occa- 

 sion. We continued in the Gulf-stream until shortly after mid- 

 night on the 25th, when a sudden change in the temperature of 

 the surface of the sea from 22°-2 C. to 18° C. showed that we 

 had crossed its southern limit. In crossing the Gulf-stream in 

 both directions, the alternate bands or interdigitations of warm 

 and cold water were very perceptible. Ilalf-hourlj^ temperature 

 observations were taken (Appendix D), and the diagram Plate 

 XII. is constructed from the general results. 



In a former volume ("• The Depths of the Sea," Chapter 

 VIII.), I have given a general account of the Gulf-stream, and 

 I have entered somewhat fully into the recent controversies i-e- 

 garding its origin and influence. Since that book was written, 

 greater harmony of opinion appears to obtain on these points. 

 It seems to be generally admitted that the Gulf-stream is due 

 to the reflux of the equatorial current, and that it is not in any 

 sense a modifled case of a general ocean circulation produced 

 by convection ; and most physical geographers seem to l)e at 

 one as to the very important influence which it exerts in dis- 

 tributing and accumulating tropical warmth in the North At- 

 lantic, and in ameliorating the climatic conditions of the coun- 

 tries which border its eastern shores. We have since had an 

 opportunity of tracing the distribution of temperature in the 

 corresponding region of the North Pacific, and the comparison 

 between the two is very instructive. The differences between 

 them are great, but when carefully considered they are found 

 to be more differences in dem-ee than in kind. 



In the Pacific the ocean area is of course vastly greater than 

 in the Atlantic, and the equatorial current is to the full as 



