132 LIGHT SCIENCE FOR LEISURE HOURS. 



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 Richmond, 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 Graves- 

 end. 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 ^vrhich is but 

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

 width certainly not less than thirtyfold would appear 

 to correspond 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 

 hundred yards, we could scarcely assign to the wide 

 current in the mid-Atlantic a greater depth than ten 

 or twelve yards. This depth seems altogether out of 

 proportion to the enormous lateral extension of the 

 current. 



