2l6 LIGHT SCIENCE FOR LEISURE HOURS. 



The accompanying map exhibits the nature of the 

 surface circulation of the North Atlantic. It is con- 

 structed on one of the forms of equal-surface projection 

 described in my ' Essays on Astronomy,' and has the 

 advantage over the ordinary Mercator's charts of ex- 

 hibiting the true dimensions of the various currents. 

 I would, however, invite the student who wishes to fa- 

 miliarise himself with the true nature of the Atlantic 

 currents to construct other maps ; for instance, a polar 

 map on the first method of equal-surface projection 

 described in that essay (see pp. 264, 265), and a map of 

 the whole Atlantic on the second plan, taking the 

 meridian 40 west of Greenwich as the central one. 



Of the water carried westwards by the great equa- 

 torial movement, the most important portion after 

 reaching Brazil is carried northwards towards the West 

 Indies. The reason of this is obviously to be found 

 in the fact that Cape San Roque, forming the jutting 

 angle of Brazil, lies several degrees south of the equa- 

 tor. The portion carried southward forms the Brazil 

 Current, and after travelling along the shores of South 

 America almost as far as the mouth of the La Plata, 

 acquires gradually an eastwardly motion which eventu- 

 ally carries it back across the Atlantic towards the Cape 

 of Good Hope, there to pass northwards, and so again 

 to traverse the Bight of Biafra. The surface-circula- 

 tion in the South Atlantic is thus seen to be com- 

 paratively simple. 



The larger portion of the equatorial current is carried 

 less quickly northward, because the northern shore-line 



