in the Air and in the Sea. 99 



seek to proceed in the direction in which the force acts that pro- 

 duces the motion, therefore in that of the meridian. Now, ac- 

 cording to the existing theory, two forces are constantly acting 

 both upon trade-winds and the meridional currents of the ocean : 

 — of which the one, the impelling force, springs from the differ- 

 ence of temperature of the equatorial and polar regions, and 

 hence operates only in the meridian-direction ; while the other, 

 the rotating force of the earth, acts in consequence of the inertia 

 of the particles, and always in the direction of the parallel circle, 

 therefore at right angles to the motive force. If, then, both 

 forces remained constantly unaltered, the direction of the current 

 would also remain invariably the same ; that is, the angle which 

 the current forms with the meridian would neither increase nor 

 diminish. In our case the action of the force in the meridional 

 direction must be assumed to be constantly uniform ; while the 

 lagging behind, or the advance, called forth by the transition 

 into other latitudes is more considerable in the higher than in the 

 lower latitudes, because the parallel circles diminish only very 

 gradually in the latter, but rapidly in the former. From this 

 it follows that the deviation from the meridional direction would 

 necessarily be greatest in the high latitudes, ancj vice versa. 

 Every current, of air or sea, springing from difference of tem- 

 perature would therefore, when flowing toward the equator, come 

 constantly nearer to the direction of the meridian ; while a cur- 

 rent flowing away from the equator must be continually adding 

 a little to the angle which it forms with the meridian. Accord- 

 ing to Hadley's theory, the trade-winds, flowing to the equator, 

 should therefore be continually approximating nearer to the 

 direction of the meridian; instead of which we see just the op- 

 posite — that at their polar limit they blow from the north-east or 

 south-east, according to the hemisphere, and as they near the 

 equator they come ever nearer to coincidence with the direction 

 of the parallel circles. 



The sea-currents of the southern hemisphere also demonstrate 

 that the earth's rotation has but little, if any, influence on the 

 direction of currents. The warm currents (those of Brazil and 

 Mozambique) lean to the east coasts of the continents, and are 

 directed to the south-west, instead of deviating eastwards ; while 

 the cold currents (those of Peru and South Guinea, and the 

 general current of the entire Antarctic Ocean) agree in directing 

 their course to the north-east, instead of flowing south-west as 

 required by the theory of the deviation of direction arising from 

 the rotation of the earth. We see in this circumstance a proof 

 that the influence of the rotation is in the whole very little, 

 although the direction taken by the currents of the northern 

 hemisphere appears to correspond entirely with that theorv : 



112 



