II 6 LIGHT SCIENCE FOR LEISURE HOURS. 



reason, how this narrow current can be looked upon as 

 the parent of that wide stream which is supposed to- 

 traverse the Atlantic with a mean width of some five 

 or six hundred miles. Indeed, a much greater width 

 has been assigned to it, though on mistaken grounds ; 

 for it has been remarked that since waifs and strays 

 from the tropics are found upon the shores of Portugal, 

 as well as upon those of Greenland, we must ascribe 

 to the current a span equal to the enormous space 

 separating these places. But the circumstance here 

 dwelt upon can clearly be explained in another way. 

 We know that of two pieces of wood thrown into the 

 Thames at Eichmond, one might be picked up at 

 Putney, and the other at Gravesend. Yet we do not 

 conclude that the width of the Thames is equal to the 

 distance separating Putney from Gravesend. And 

 doubtless the tropical waifs which have been picked up 

 on the shores of Greenland and of Portugal have found 

 their way thither by circuitous courses, and not by 

 direct transmission along opposite edges of the great 

 Gulf current. 



But certainly the difficulty associated with the nar- 

 rowness of the Bernini current is one deserving of 

 careful attention. Are we free to identify a current 

 six hundred miles in width with one which is but thirty 

 miles wide, and not very deep ? An increase of width 

 certainly not less than thirtyfold would appear to cor- 

 respond to a proportionate diminution of depth. And 

 remembering that it is only near the middle of the 

 Narrows that the Gulf Stream has a depth of four 



