in the Air and in the Sea. 171 



mal level of the sea than the ebb sinks below it, we think we 

 can assume, as an hypothesis, that the force of the flood-current 

 will also be greater than that of the ebb-current. 



In our case, if the cusps of the ellipsoid are on the equator, 

 and therefore both forces develop their maximum on that circle, 

 the greater force must overpower the smaller, and both in air 

 and sea a current from east to west must prevail all along the 

 equator. On both sides of the equator the force of the flood- 

 current, acting from east to west, diminishes rapidly polewards ; 

 the counteracting force of the ebb-current diminishes more 

 slowly. Therefore, at a certain distance from the equator, the 

 greater but rapidly diminishing force directed from east to west 

 will be only just as great as the smaller only slowly decreasing 

 force directed from west to east. In these parallels the forces, ba- 

 lancing each other, will generate no current. Still further pole- 

 wards the force of the flood-current, still continually more de- 

 creasing, will be less than that of the ebb-current, and, both in 

 the sea and in the atmosphere, currents from west to east will 

 make their appearance. In the latitude of the points m the 

 east-to-west force ceases entirely ; while the opposite force has 

 in this latitude lost only a small portion (less than half) of its 

 action, and hence may here produce a considerable current. In 

 higher latitudes the force of the ebb-current will also quickly 

 diminish, and the currents from the west become considerably 

 less, and their direction probably turn more towards the equator. 

 Accordingly, in the northern hemisphere, in high latitudes, cur- 

 rents will arise from the north-west, and in the southern from 

 the south-west. 



When, therefore, the moon and sun are at the same time in 

 the vicinity of the equator, a current in air and sea must flow 

 there from east to west. On both sides of the equator this cur- 

 rent will diminish polewards until it entirely ceases; and there 

 must thus be produced a streamless zone parallel to the equator. 

 Further polewards a west-to-east current will prevail, which 

 must at first increase gradually until it attains its maximum ; 

 then will this current also again diminish gradually, and in high 

 latitudes flow from the north-west in the northern hemisphere, 

 and from the south-west in the southern. 



In reality we find this to be the constitution of the currents. 

 In middle latitudes constant west winds and sea-currents directed 

 eastwards prevail. In the latitude of about 30° there is in each 

 hemisphere a zone of no current, and in the tropical regions we 

 find currents flowing perpetually from east to west, both in air 

 and sea. An apparent exception is, that on the equator we 

 meet with a zone in which no current is perceptible either in the 

 atmosphere or in the ocean. 



