122 LIGHT SCIENCE FOR LEISURE HOURS. 



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 neigh- 

 bouring 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 northward 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 tempe- 

 rature, 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 

 temperature; and arguments on the subject of the 

 Gulf Stream have been derived from the evidence of 

 what is termed a minimum thermometer that is, a 

 thermometer which will indicate the lowest temperature 

 it has been exposed to let down into the depths of 

 the sea. All such arguments, whether adduced against 

 or in favour of the Gulf Stream theory, must be held, 



