§ 95, 9G. THE GULF STREAM. 



29 



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

 likened to the jet, and the Atlantic to the pool. We remem- 

 ber to have observed as children how soon the mill-tail loses its 

 current 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 swal- 

 lowed up in the lake. 



95. Nothing but a continually-acting power can keep currents 

 Gulf stream the ef- ^^ the sca, any more than cannon balls in the air or 

 Santiy '"o'ljeratog ^'ivcrs ou 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 caldron, as the 

 intertropical parts of the Atlantic Ocean may be called. 



96. For the sake of further illustration, let us suppose a globe 

 The production of of the carth's size, and with a solid nucleus to be 



currents without in • ^ 



>v^iiid. covered all over with water two hundred fathoms 



deep, and that every source of heat and cause of radiation be re- 

 moved, so that its fluid temperature becomes constant and uni- 

 form throughout. On such a globe, the equilibrium remaining 

 undisturbed, there would be neither wind nor current. Let us 

 now suppose that all the water within the tropics, to the depth 

 of one hundred fathoms, suddenly becomes oil. The aqueous 

 equilibrium of the ])].inet would thereby be disturbed, and a gen- 

 eral system of currents and counter currents would be immedi- 

 ately commenced — the oil, in an unbroken sheet on the surface, 

 running toward the poles, and the water, in an under current, to- 

 ward the equator. The oil is supposed, as it reaches the polar 

 basin, to be reconverted into water, and the water to become oil 

 as it crosses Cancer and Caj^ricorn, rising to the surface in the in- 

 tertropical regions and returning as before. Thus, withoiit ivind^ 

 we should have a perpetual and uniform system of tropical and 

 polar currents, though without wind^ Sir John Herschel main- 

 tains,* we should have no currents whatever in the sea. In conse- 

 quence of the diurnal rotation of the planet on its axis, each particle 

 of oil, were resistance small, would approach the poles on a spiral 

 turning to the east with a relative velocity greater and greater, 



* " If there were no atmosphere, there would be no Gulf Stream or any other 

 considerable oceanic current (as distinguished from a mere surface drift) whatever." 

 — Art. 37, Physical Geography^ 8th ed. Encyclop. Brit. 



