196 LIGHT SCIENCE FOR LEISURE HOURS. 



course and habitudes of this current, and then to inquire 

 a little into the vexed question of its cause. 



Major Eennell traced the Gulf Stream from a sup- 

 posed source in the Indian and Southern Oceans. 

 Modern geographers and physicists prefer to look for 

 the rise of the current somewhere near the Cape of 

 Good Hope. ' The commencement and first impulse 

 of the mighty Gulf Stream is to be sought,' writes 

 Humboldt, ' southward of the Cape of Good Hope.' 

 It appears to me, however, that the true source of the 

 great stream is to be looked for in the equatorial zone 

 of the Atlantic. When we come to inquire into the 

 cause or causes which give birth to the Gulf Stream, 

 we are led, as I imagine, to this region rather than to 

 any other (though, perhaps, in a stream which forms 

 part of a continuous system of circulation, we can 

 hardly speak of any one portion as the source) ; I shall 

 therefore trace the stream, and the system to which it 

 belongs, from the great equatorial waters which move, 

 as Columbus was the first to discover, 4 with the heavens 

 (las aguas van con los cielos)., that is, from east to 

 west, following in this the apparent motions of the sun, 

 moon, and stars.' 



The map of the Atlantic Ocean on p. 217, is con- 

 structed upon one of those forms of isographic pro- 

 jection described in my Essays on Astronomy. It is 

 important, in dealing with the subject of currents, that 

 the question of area should be considered, and, there- 

 fore, that our illustrative charts should represent such 

 areas correctly. This Mercator's charts are far from 



