34 Baron N. Schilling on the Constant Currents 



flowing must rapidly diminish downward, and soon entirely 

 cease. A. Findlay"* thinks that the wind can never call forth 

 a current of greater depth than 5 fathoms. James Croll's re- 

 mark f, that the duration of the wind, as well as its force, must 

 have great influence on the depth to which it acts, may to a 

 certain extent be quite correct ; but, nevertheless, action of the 

 wind upon currents at a depth of thousands of feet (as, for in- 

 stance, in the equatorial current) is not possible; hence we 

 must see that Franklin and RennelFs view, that the equatorial 

 current results from the action of the trade-winds, cannot be 

 true. 



Nature herself gives us decisive proofs against that view. 

 With the shifting of the zone of calms it happens that the 

 equatorial current flows just as well in that zone as in the trade- 

 wind. In the Indian Ocean the change of the monsoons has 

 scarcely any influence on the equatorial stream. The Gulf- 

 stream often flows in opposition to very violent storms, which 

 would be impossible if its motive force lay in the trade-wind. 



Even the opinion that the trade-wind raises the level of the 

 Gulf of Mexico, and so produces the Gulf-stream, is untenable. 

 In the first place, it is proved by the levelling of the isthmus of 

 Panama and the peninsula of Florida that this is not the case, 

 as the level of the Mexican Gulf pretty closely accords with 

 both that of the great ocean and that of the Atlantic. Secondly, 

 in the open sea an enduring higher level can never be produced 

 by the action of the wind ; for as soon as any particles of water, 

 driven by the wind, change their place, they compel by their 

 pressure just as many others immediately to take the place left 

 free by them. Only where the formation of the coast hinders, 

 or at least impedes, this back-flowing motion, can an alteration 

 of level take place. 



Certainly the mechanical pressure of the wind upon the sur- 

 face of the water can, in the open sea, somewhat alter the level; 

 but as the wind mostly acts horizontally, or at a very acute 

 angle, upon the surface, the mechanical pressure is so little 

 that the oscillations of the sea-level brought about by it must 

 likewise be inconsiderable. 



Just so must the variations of the atmospheric pressure exert 

 an influence on the height of the water of the seas, and con- 

 sequently also on their currents. When, for example, the 

 barometer falls an inch, the surface of the sea at the place must 

 rise 13*6 inches, and vice versa, and thus a current be formed 

 from where the pressure is high to the region where lower pres- 



* A Dictionary for Navigation of the Pacific Ocean (London, 1851), 

 vol. ii. p. 1222. Also Miihrv, Geograph. Miitheilungen, 1872, p. 136. 

 t Phil. Mag. October 187*1, p. 268. 



