THE GULF STREAM. 31 



its shores, require that the impulse then and there comnmnicatecl 

 to the ^Yaters of the Grulf' Stream should be 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 ex- 

 pended ? 



94. When we inject water mto a pool, be the force never so 

 Illustration. great, the jet is soon overcome, broken up, and 



made to disappear. In this 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 ^Ye 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 below. 



95. Xothing but a continually-acting power can keep currents 

 Gulf stream the iH the sea, any more than cannon-balls in the air or 

 Sn'th^lpm^^^ rivers on the land, in motion. But for the forces 

 power. 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 fm^ther illustration, let us suppose a globe 

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



currents without t n -n i j i n t n n 



wind. covered ail over with water two hundred lathome 



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 remaming 

 undistm-bed, 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 planet woidd thereby be disturbed, and a gene- 

 ral system of ciuTents and counter currents would be immediately 

 commenced — the oil, in an unbroken sheet on the surface, run- 

 ning towards the poles, and the water, in an under ciuTent, to- 

 wards 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 Capricorn, rising to the surface in the in- 

 tertropical regions, and retmiiing as before. Thus, ivithout wind, 

 we should have a perpetual and uniform system of tropical and 

 polar currents, though ivitJioiit wind, Sir John Herschel main- 



