98 Baron N. Schilling on the Constant Currents 



this deviation arising from the earth's rotation that, in the 

 northern hemisphere, all the rivers which run in a meridional 

 direction undermine their right banks — through which these 

 banks are the high, but the left the low ones. The whirling 

 motion of cyclones, or Buys-Ballot's law, and the deviation of 

 the meridional currents of the ocean, are all explained by the 

 axial rotation of the earth. 



It is indubitable that the direction of every independent mo- 

 tion on the surface of the earth receives, through its rotation, a 

 certain tendency to deviation; yet it seems to us that the 

 amount of this deviation is only too often greatly overrated. It 

 is usually assumed that, in consequence of inertia, air and water 

 particles can retain for hours the velocity of the parallels which 

 they have long left behind. In reality, however, the friction 

 and resistance of other particles will more speedily overcome the 

 inertia and compel the particles in motion soon to take up the 

 new rotation-velocity of the parallel circles which they enter. 

 It must also be remembered that the velocity of adjacent paral- 

 lels only very gradually changes; and therefore, with a slow 

 motion of the particles, the least friction will be sufficient to 

 overpower the difference existing between neighbouring parallels. 

 The true proportion between the friction and the tendency to 

 conserve the earlier rotation-velocity is very difficult to determine 

 accurately; nevertheless it seems clear to us that the deviation 

 thereby occasioned in the direction of motion in a short time 

 iiust always be very inconsiderable. The defenders of Hadley's 

 theory will admit this, although they generally believe that, by 

 itself slight, the deviation can, by continual repetition of the 

 action, accumulate and so become gradually considerable. They 

 think, namely, that a current of air or sea, originated by differ- 

 ence of temperature, flowing along the meridian, would, when a 

 little deflected by the earth's rotation, continue to flow in this 

 new direction, and so on. In other words, it is generally be- 

 lieved that the angle which a current makes with the meridian 

 must continually increase with the duration of the current ; and 

 some go so far as to see, not only in the south-west wind of the 

 middle latitudes of our hemisphere, but even in the north-west 

 wind of the same, an antipolar current diverted from its direc- 

 tion by the rotation of the earth. But this evidently false con- 

 clusion results from the false assumption that a current once 

 deflected would continue to flow in the new direction. It is 

 forgotten that the rotation of the earth cannot effect a deviation 

 of the direction unless a motion is present. If the motive force 

 ceased to act, the current would soon cease also, being over- 

 powered by friction and other resistance. It cannot, therefore, 

 flow further in the deflected direction, but will always again 



