in the Air and in the Sea. 109 



in the direction of the southern hemisphere occasions there, 

 according to Schmick, an accumulation of the waters. That 

 the centre of gravity, displaced by external force, cannot of 

 its own accord resume its former position is perfectly true; 

 only Dr. Schmick seems to have forgotten that if the water 

 rises higher on the hemisphere turned towards the moon than 

 on the opposite, it is because it is lighter there on account of the 

 greater attraction of the moon, and a greater gathering of the 

 lighter water is necessary in order to restore equilibrium, with- 

 out displacing the centre of gravity. If, therefore, the entire 

 globe consisted of a liquid and had no rotation, the moon's at- 

 traction would cause it to take the form of an ellipsoid, of which 

 the cusp directed to the moon would be somewhat higher than 

 the cusp turned away from it ; but the centre of gravity of the 

 entire mass would remain undisturbed in its old place, because, 

 as already said, the rise of the water on each point must be 

 exactly equivalent to its loss of weight. As, however, the earth 

 consists, for the most part, of a solid mass, which cannot alter 

 its shape, and the hemisphere turned to the sun and moon loses 

 more of its weight than the opposite one, the centre of gravity 

 must be displaced in the opposite direction to that supposed by 

 Dr. Schmick ; namely, it must remove to a somewhat greater 

 distance from those bodies. Of course the displacement is only 

 very inconsiderable, even when the moon is at its least distance 

 from the earth ; yet it may to some extent favour temporary 

 variations of the atmospheric pressure. In the moon, which 

 constantly shows one side to the earth, the earth's attraction 

 must thus cause the centre of gravity to lie permanently on the 

 side which is turned away from us. 



When the tidal wave does not attain its greatest height at the 

 time required by the moon, or in consequence of collateral cir- 

 cumstances attains a far greater height than the moon's at- 

 traction demands (as in the Bay of Fundy, the English Channel, 

 and many other places), the earth's centre of gravity will cer- 

 tainly remove temporarily in the direction of the elevation of the 

 waters; but Schmick's view*, that the water must spread over 

 the surface in accordance with the new centre of gravity as soon 

 as the accumulating force ceases, cannot be regarded as correct, 

 because any excessive accumulation of the water is followed by 

 an equal sinking of the level. The earth's centre of gravity 

 must follow these oscillations of the water, and hence, when this 

 gradually comes to rest, will probably have returned to its old 

 position. 



[To be continued.] 



* Fhith'Phanomene, p. 128. 



