124 LIGHT SCIENCE FOR LEISURE HOURS. 



monly supposed that a bed of ordinary sea-water 

 separates the two main currents from each other. Thus 

 the characteristic difference of temperature remains 

 unaffected. But in reality we may assume that the 

 cooling effect actually exercised by the arctic current 

 upon the neighbouring sea is altogether disproportionate 

 to the immense amount of heat continually being 

 carried northwards by the Gulf Stream. It is as- 

 tonishing how unreadily two sea-currents exchange 

 their temperatures to use a somewhat inexact 

 mode of expression. The very fact that the littoral 

 current of the United states is so cold a fact 

 thoroughly established shows how little warmth this 

 current has drawn from the neighbouring seas. Another 

 fact, mentioned by Captain Maury, bears in a very 

 interesting manner upon this peculiarity. He says : ( If 

 any vessel will take up her position a little to the north- 

 ward of Bermuda, and steering thence for the capes 

 of Virginia, will try the water-thermometer all the 

 way at short intervals, she will find its reading to be 

 now higher, now lower ; and the observer will discover 

 that he has been crossing streak after streak of warm 

 and cool water in regular alternations.' Each portion 

 maintains its own temperature even in the case of such 

 warm streaks as these, all belonging to one current. 



Similar considerations dispose of the arguments 

 which have been founded on the temperature of the 

 sea-bottom. It has been proved that the living creatures 

 which people the lower depths of the sea exist under 

 circumstances which evidence a perfect uniformity of 



