292 



SCIENCE. 



[Vol. X. No. 254 



Society. The trade-winds, he says, produce not only dry places 

 on the land, but also comparatively dry places on the sea, and 

 therefore the areas of maximum density or salinity of the surface- 

 water are situated in the trade-winds region. In passing over the 

 surface of the ocean, the winds impart motion to the water imme- 

 diately under their influence. The effect of this is to produce a 

 general motion of the denser intertropical water towards the equa- 



west coast of North Africa the line of 24° C. (75° F.) extends far 

 southward. Similar phenomena occur on the west coast of Ameri- 

 ca. Formerly the reason for the low temperature of these waters 

 was looked for in polar currents, but recent observations show that 

 it is caused by cold water of deeper layers rising to the surface.. 

 So far as we are aware, E. Witte was the first to express this opin- 

 ion, in a paper published in 1878; but recently a considerable 



MAP OF THE PACIFIC OCEAN, SHOWING THE SURFACE-TEMPERATURES IN AUGUST (ACCORDING TO O. KRUMMEL). 



tor and towards the west. At the same time the surface-water is 

 evaporated, and thus becomes more concentrated than the deeper 

 and colder layers. In consequence of its greater salinity, the warm 

 surface-water sinks to a certain depth, and thus conveys its higher 

 temperature to the deeper layers. Thus the western parts of the 

 ocean are supplied with water of high temperature, which is col- 

 lected in the Atlantic Ocean in the immense bay formed by the 

 coasts of North and South America. 



Another remarkable fact is shown in our map. It is the preva- 

 lence of cold water along many coasts. In South Africa we see 

 the line of 16° C. (61° F.) extending far northward, and on the 



amount of material has been contributed by numerous investiga- 

 tors. Among these, I mention Buchanan's researches in the region 

 of the counter equatorial current on board the 'Buccaneer,' Cap- 

 tain Hoffmann's observations off Cape Guardafui, and Dr. G. Stapff's 

 off Angra Pequena in South Africa. All these observations tend 

 to show, that wherever the prevailing winds are blowing off the shore, 

 and the water is thus removed without a possibility of being replaced 

 by superficial currents, cold water rises to the surface. But it -has 

 been pointed out in an essay published in the Anjtalett der Hydro- 

 graphie, that, wherever a current is deflected from a coast, cold' 

 water must rise to the surface. This fact accounts for the low 



