54 CAUSE OF THE GULF STREAM. 



the waters of the ocean in some places more than in 

 others ; hence the equilibrium is destroyed, and cur- 

 rents commence to flow as a natural result, seeking to 

 restore that equilibrium. But as the disturbing agents 

 are always at work, so the currents are of necessity 

 constant.' Other currents there are in the sea, but 

 they are the result of winds and various local causes ; 

 they are therefore temporary and partial, while the 

 great currents of the ocean are permanent, and are, 

 comparatively, little affected by the winds. Every 

 one knows that when a pot is put on the fire to boil, 

 the water contained in it, as soon as it begins to get 

 heated, commences to circulate. The heated water 

 rises to the top, the cold descends. When heated 

 more than that which has ascended, it in turn rises 

 to the surface; and so there is a regular current 

 established in the pot, which continues to flow as 

 long as the heating process goes on. This same 

 principle of temperature, then, is one of the causes 

 of the Gulf Stream. The torrid zone is the furnace 

 where the waters of the ocean are heated. But in 

 this process of heating, evaporation goes on to a 

 large extent ; hence the waters become salter than 

 those elsewhere. Here is another agent called into 

 action. The hot salt waters of the torrid zone at once 

 rush off to distribute their superabundant caloric 

 and salt to the seas of the frigid zones ; where the ice 

 around the poles has kept the waters cold, and the 

 absence of great heat, and, to a large extent, of 

 evaporation, has kept them comparatively fresh. 



