498 



CAUSES OF CURRENTS. 



[Ch. 



by a sluice or partition, have one end filled with water and 

 the other with quicksilver, both fluids will remain quiet so 

 long as they are divided ; but when the sluice is drawn up, 

 the°heavier fluid will rush along the bottom of the trough, 

 while the lighter, being displaced, will rise, and, flowing in 

 an opposite direction, spread itself at the top. 



We 



north having a temperature of only 40° Fahr., passes in lat. 

 40°30'N. under the Gulf-stream, which, having a temperature 

 of 80° Fahr., runs above it in exactly an opposite direction. 

 A striking example will be given in the next chapter, p. 562, 

 of the effect of a submarine barrier in preventing the lower 



from the neighbouring 



om ben 

 ocean. 



One of the chief oceanic 

 currents is that which flows through the Mozambique Chan- 

 nel, and there skirts the south-east coast of Africa, having a 

 breadth of ninety miles and a velocity of between two and four 

 miles an hour. On reaching the Cape, it is turned westward 

 by the Lagullas, a great shoal or rather a submerged chain 

 of mountains, which, rising from a deep ocean, comes within 

 100 fathoms of the surface. The deflection of this current, 

 says Eennell, proves that it is more than 100 fathoms 

 deep, otherwise the main body of it would pass across the 

 bank instead of being deflected westward, so as to flow 

 round the Cape of Good Hope. It is then joined by a cur- 

 rent from the south or from antarctic latitudes, and, con- 



tinuin g 



its course, takes a northerly direction 



along 



the 



western coast of Africa, till it reaches the Bight or Bay of 

 Benin. There it is turned westward, partly by the form of 

 the coast and partly perhaps by meeting the Guinea current, 



u a a ^ I J * *w/% m\ a 1 1 



From 



which runs from the north into the same great bay. 



the centre of this bay proceeds what is called the equatorial 



current of the Atlantic, having a width of from 160 to 450 



miles, and holding a westerly course across 



that 



ocean which it traverses from the coast of Guinea to that of 

 Brazil. The whole length is said to be about 4,000 geogra- 

 phical miles, and its velocity from twenty-five to seventy- 

 nine miles per day, the mean rate being about thirty miles. 

 On approaching the N.E. promontory of South America, 







. 



I 





be 



