26 Baron N. Schilling on the Constant Currents 



rapid, the polar wind is turned westward, and expresses itself in 

 the northern hemisphere by a north-east, in the southern by a 

 south-east wind. In the higher strata the ascending air returns 

 to the poles to serve as a compensation for the air which has 

 flowed thence to warmer latitudes. As this upper anti-trade 

 streams polewards, it receives from the rotation of the earth a 

 deflection eastward in both hemispheres. Compressed by cool- 

 ing and the polar convergence of the meridians, it sinks at about 

 the latitude of 30° to the surface of the earth and so forms the 

 constant west wind of the middle latitudes. The ascent of the 

 air at the equator and its descent in 30°lat. will produce in the 

 first case the equatorial calms, and in the second the calms of 

 the tropical zones. 



This is, as briefly as possible, the generally recognized theory 

 of the trade-winds, which, however, is not at all adapted for ex- 

 plaining the perfectly analogous rotation-currents of the ocean. 



The equatorial current is still regarded by many as a drift- 

 stream produced by the trade-winds. This already long-per- 

 sistent opinion received such a confirmation by the authority of 

 Franklin and Rennell, that, notwithstanding its forcible refuta- 

 tion by Maury and Miihry, it is still maintained, although only 

 in England. For instance, Herschel, Carpenter, and Laugh- 

 ton have recently pronounced in favour of this explanation. 

 Far more prevalent, however, is now the view that the cause 

 of the equatorial current is to be sought immediately in the 

 axial rotation of the globe. Columbus, the discoverer of this 

 current (in 1492), accounted for it by the universal motion of 

 the heavens [con los cielos) from east to west*. This notion of 

 the " primum mobile " was followed by all, till Kepler at the 

 commencement of the 17th century pointed out, and Varenius 

 (1650) proved in detail, that the current was occasioned not by 

 the "primum mobile/' but by the rotating motion of the earth, 

 the water not being able to keep up with the earth's rapid mo- 

 tion. Miihry, the chief authority on ocean-currents, substanti- 

 ally shares this view, only giving to it a different and not quite 

 intelligible expression. He saysf; as Fourier J before him, that 

 the staying behind of the water is effected by the centrifugal 

 force of the earth. By this expression we are accustomed to 

 understand the force that throws off from the centre, which 

 always acts in the direction of the radius of each parallel circle ; 

 and hence we cannot see how this force could cause the swift- 

 ness of rotation of the water to be less than the rotation-velocity 

 of the entire globe. 



* Kohl, Geschichte des Golfstroms, p. 30. 



t Ueber die Lehre von den Meeres-Stromungen, p. 5. 



J Ann. de Chim. et de Phys. 1824.. p. 140. 



