464 Dr. Werner Siemens on the Conservation 



It follows at once from these considerations that with in- 

 creasing geographical latitude the frequency and strength of 

 the air-currents in the direction of the earth's rotation — that 

 is, in our hemisphere, the west winds — must increase rapidly. 

 In the arctic regions themselves, the highest strata of the 

 equatorial current, which alone can reach so far without 

 having been compelled to return, must flow downwards to 

 the earth's surface in north-easterly spirals. Hence, and 

 from the rush on all sides towards the pole, they must pro- 

 duce an arctic maximum, and after sinking with preservation 

 of their velocity must commence their return to the equator 

 as a lower north-west wind. It is therefore again the vis viva 

 obtained in the equatorial impulse which also drives back the 

 air from the polar regions to the equator, and not the action 

 of doubtful gradients of air-pressure, which are by no means 

 sufficient for the explanation of the phenomena. By friction 

 with the earth's surface the south-east velocity which this 

 return-branch of the equatorial current everywhere possesses 

 is soon considerably diminished, and at the surface of the 

 earth itself would soon be altogether destroyed if the higher 

 strata of air of the return-current did not maintain it. In con- 

 sequence of the expansion of the lower current-bed, which 

 takes place rapidly in the higher latitudes, a rarefaction is 

 produced in the mean strata of air, advancing more rapidly 

 towards the equator, which brings about an inflow of the re- 

 latively quiet lower strata of air into the higher ones rarefied 

 beyond the condition of neutral equilibrium. This inflow 

 must take place from lower latitudes, because in them the 

 difference of pressure causing the impulse, in consequence of 

 expansion of the current-bed, is a smaller one. Hence the 

 current on the earth's surface, even in the northern hemi- 

 sphere, must acquire a southerly component. This explains 

 why, as experience shows is the case, the south-west, and not 

 the north-west, has here the mastery, as must be the case in 

 the higher strata of the return-current. 



Also in the hypothetical case so far discussed, of a homo- 

 geneous smooth and dry earth's surface, the motions of the 

 air in mean and high latitudes must be altogether irregular, 

 and by no means to be determined beforehand, since the 

 maxima and minima commenced and maintained by blocking, 

 and the carrying on of relatively quiescent air by that in 

 more rapid motion, serve as accumulators of the kinetic energy 

 of the upper air-current, the charging and discharging of which 

 must always cause new disturbances of the equilibrium of the 

 atmosphere, and must produce air-currents circling up and 

 down in it. In fact, the very unequal distribution of land 



