168 Baron N. Schilling on the Constant Currents 



circles of normal level are more than 45° and less than 60° of 

 arc distant from the cusps of the tidal ellipsoid*. 



As at coasts the currents produced by the flow and ebb are 

 always observed to flow alternately in precisely opposite direc- 

 tions, it is generally believed that the attraction of the moon and 

 sun cannot exert any influence on the constant currents. Miihry 

 says, " It is scarcely necessary to mention that the tidal motion, 

 which daily carries its two meridian waves round the globe, is 

 something altogether different from the rotation-current : the 

 former extends over all latitudes, and generally occasions no 

 forward motion of the mass of water, but only waves, i. e. oscil- 

 lations .... Such an assumption is contradicted also in a pe- 

 culiarly decided manner by the return- currents flowing on both 

 sides of the equatorial current in a wide semicircle from west to 

 east (therefore against the tide-wave) — the compensation-arms 

 of the rotation- current, which at the same time enclose each a 

 wide central space filled with still water and floating seaweed, 

 the Sargasso-seas. How can the tide-wave call forth such phe- 

 nomena? "We are of opinion, moreover, that, if there were no 

 moon_, the equatorial current would still exist while the earth 

 revolved on its axis ; but it would not exist if the globe did not 

 turn on its axis, even though the moon should daily travel round 

 the earth "f- 



We cannot possibly share this opinion of Muhry's. We will 

 besides let the thing speak for itself, subjecting the action of the 

 attraction of the sun and moon to a closer consideration. 



Suppose the circle AGED (fig. 4) to be the equator, and 

 L the centre of the moon, which we will imagine in the plane of 

 the equator. If, then, the earth had no rotation, the surface of 

 the sea must take the form of the dotted line aced. To form 

 this ellipsoid, currents must proceed from all sides towards the 

 cusps a and e, lasting until the ellipsoid had attained its due 

 elongation. But since the earth is constantly turning, the moon 

 relatively to the earth will have already arrived at another point 

 before the water and the atmosphere have had time to properly 

 form the ellipsoid aced. Of course the currents will immedi- 

 diately direct their course to the new point of attraction ; and 

 since this again alters its position, a current must be produced 

 in the air and water which must endeavour to follow the motion 

 of the moon and shift the cusps of the ellipsoid perpetually from 

 east to west. On the other hand, by the shifting of the moon 



* It appears, therefore, that the zero-point of the tide-gauges has not 

 yet received its true position. This must lead to erroneous results in level- 

 ling-surveys when the heights of two neighbouring seas are to be compared 

 in which the heights of the tides differ (as, for instance, Panama). 



t Muhry, Ueber die Lehre von den Meeres-Stromungen, p. 9. 



