32 rnTSiCAL GEOGKArnY of the sea, and its meteorology. 



thousand (§ 75) such streams as the ]Mississippi liiver — a powei 

 at least sufficient to overcome iho resistance required to reduce 

 from two miles and a half to a few feet per minute the velocity 

 of a stream that keeps in perpetual motion one-fourth of all the 

 waters in the Atlantic Ocean. Xot onl}^ so, we must admit the 

 existence of an engine in the Gulf of IMexico, which, being 

 played upon b}' the gentle forces of the trade-winds, is capable of 

 sending a stream of water from the shores of the Kew A\'orld to 

 the shores of the Old. 



93. I^or hy the trade-wind theory. — The advocates of the trade- 

 wind theory, whether, with Franklin (§ 77), they make the 

 propelling power to be derived from a ''head of water'' in the 

 Gulf, or, with Herschel (§ 79), from the rebound, a la billiard- 

 balls, against its shores, require that the impulse then and there 

 communicated to the waters of the Gulf Stream should bo 

 sufficient to send them entirely across the Ocean ; for in neither 

 case does their theory provide for any renewal of the propelling 

 power by the wayside. Can this be ? Can water flow on any 

 more than cannon-balls can continue their flight after the 

 propelling force has been expended ? 



94. Illustration. — When we inject water into a pool, be the 

 force never so great, the jet is soon overcome, broken ujd, and 

 made to disappear. In this illustration the Gulf Stream may be 

 likened to the jet, and the Atlantic to the pool. We remember 

 to have obserA-ed as children how soon the mill-tail loses its cur- 

 rent in the pool below ; or we may now see at any time, and on 

 a larger scale, how soon the Niagara, current and all, is swallowed 

 up in the lake below. 



95. Gulf Stream the effect of some constantly operating poiver. — 

 Nothing but a continually-acting power can keep currents in the 

 sea, any more than cannon-balls in the air or rivers on the land, 

 in motion. But for the forces of gravitation the waters of the 

 Mississippi would remain at its fountain, and but for difference 

 of specific gravity the waters of the Gulf Stream would remain 

 in the ciddron, as the intertropical parts of the Atlantic Ocean 

 may be called. 



9G. TJie production of currents without wind. — For the sake of 

 further illustration, let us suppose a globe of the earth's size, 

 and with a solid nucleus, to be covered all over with water two 

 hundred fathoms deep, and that every source of heat and cause 

 of radiation be removed, so that its fluid temperature becomes 



