236 LIGHT SCIENCE FOR LEISURE HOURS. 



(that is from arctic or from antarctic regions) 4 would 

 acquire a strong westerly motion (just as the trade- 

 winds do). Thus they would generate from below the 

 great equatorial westerly current. In this upflow of cool 

 currents having a strong westerly motion, we find the 

 mainspring of the series of motions. The water thus 

 pouring in towards the equator is withdrawn from 

 beneath the temperate and arctic zones, so that room is 

 continually being made for that north-easterly surface- 

 stream which is the necessary consequence of the con- 

 tinual flow of the great westerly equatorial current 

 against the barrier formed by the American continent. 

 . . . . Captain Maury's views seem only to require 

 the mainspring or starting- force towards the west 

 which has been here suggested, to supply a complete, 

 efficient, and natural explanation of the whole series of 

 phenomena presented by the great ocean currents.' 



Four or five months later, and while the results on 

 which Dr. Carpenter subsequently based his theory of 

 the oceanic circulation were as yet unpublished, I drew 

 attention in the columns of the Daily News to the 

 comparatively limited extent of the influences due to 

 polar cold. This cause, I pointed out, ' scarcely has 

 any influence in latitudes lower than the parallel of 50 

 degrees.' 



In the year 1869 Dr. Carpenter was first led to advo- 

 cate the theory that the continual descent of cold water 

 in the Arctic Seas is the mainspring of the system of 

 oceanic circulation. He reasoned that the Arctic Seas 

 being exposed to great cold, the surface water ; descends 



