in the Air and in the Sea. 173 



sequently will have already become slightly less at the parallel 

 circles a! a and e 1 e, on which the maximum of the flood-current 

 is found. The direction of this current will also not be purely 

 from west to east, but, as the arrows C and D show, alternate 

 between W.N.W. and W.S.W. The opposite forces of the ebb- 

 and flood-current must therefore on both sides of the parallel 

 circles a a 1 and e e' balance one another and form a zone of no 

 current. 



This appears to occur in the vicinity of the equator and of the 

 parallels of 30° latitude, the zones of calms and of the Sargasso- 

 seas being found there. In the latitudes of the parallel circles 

 a a 1 and ed must be the maximum of the east- to- west flood- 

 current ; this perfectly corresponds with the phenomena of the 

 trade- winds and the equatorial currents. Polewards from the 

 streamless zone in the 30th parallel of latitude the rapidly dimi- 

 nishing force of the flood-current must be overpowered by that 

 of the ebb-current, and a constant current from west to east be 

 produced — which also actually happens ; for between the 40th 

 and 50th parallels of latitude, or thereabouts, both in the air 

 and in the water, in all oceans and in both hemispheres, a cur- 

 rent directed eastwards is constantly observed. 



Hence, it seems to us, the action of the attraction of the sun 

 and moon explains the origination of the trade- winds and anti- 

 trades with their zones of calms, and the rotation-currents run- 

 ning parallel with the equator, with the Sargasso-seas and the 

 streamless equatorial zone, considerably better than all hitherto 

 existing hypotheses. 



If our explanation of the trade- winds and equatorial currents 

 is correct, also the position and the breadth of the current-zones 

 and the strength of the currents must themselves depend entirely 

 on the position of the tidal ellipsoid or on the position of the 

 moon and sun with respect to one another and relative to the 

 earth. When, for instance, moon and sun are both very near 

 the equator, the equatorial calm-zone must be non-existent, the 

 calms of the tropics must approach towards the equator, and the 

 constant west winds blow with greater force in lower latitudes. 

 Whether all this happens is unknown to us ; yet strong west 

 winds usually rage in Europe at the times of the equinox. 

 Just so, perhaps, it sometimes happens that ships cross the line 

 without calms; but whether this chiefly coincides with the time 

 when the moon crosses the equator we know not. 



When moon and sun are at the same time in the vicinity of 

 the tropics, the current-zones must be displaced polewards, and 

 the equatorial calm-zone be especially broad. It is possible that 

 then the ebb-current may predominate in the middle of the zone, 

 and that this circumstance accounts for the west-to-east current 



