6o 



fusion that is made about the source of a river. We say that 

 the Rhine rises in Switzerland, but it would be quite inaccu- 

 rate to say that all the water which flows past Rotterdam into 

 the German Ocean has come from Switzerland. Just so, the 

 Gulf-stream is a large tributary of the current that flows past 

 our coasts, and yet it is not certain that it would make any 

 sensible difference in our climate if the isthmus of Central 

 America were to sink down so as to permit the waters of the 

 Gulf-stream to flow onward into the Pacific instead of back 

 into the Atlantic. What conclusively proves the truth of this 

 view is that the comparatively warm stratum of surface water 

 has been found to be three hundred fathoms in depth near the 

 Shetland Islands, while the Gulf-stream is not more than fifty 

 fathoms in depth at the furthest point toward the north-east — 

 that is to say, at the. nearest point to our shores — at which it 

 can be distinguished as a current. In the foregoing state- 

 ment the views of Dr. Carpenter have been given with but 

 little addition. 



The effect of the ocean on climates is two-fold. The 

 capacity of water for heat is greater — that is to say, it absorbs 

 more heat when it is heated, and gives out more heat when it 

 is cooled — than any other substance. For this reason the 

 ocean has the effect of moderating the extremes of both sum- 

 mer and winter ; it is well known that the climates of coasts 

 and islands are much more free from extremes than those of 

 the interior of continents. Besides this, the ocean has the 

 effect of distributing the heat of the tropics over the globe ; 

 this is done partly by the agency of currents, and partly by 

 the heat becoming latent in watery vapour when it is evapo- 

 rated, and being liberated in watery vapour when it is con- 

 densed. By these two agencies an immense quantity of heat 

 is transported from the tropical to the temperate and polar 

 regions, with the effect of lowering the temperature of the 

 former and raising that of the latter. There is no doubt of 



