Tidal Wave on the Earth's Rotation. 291 



the molecules of the water. Now this effect cannot take place 

 while the waters are rising; for it is the effort of the molecules 

 of the water to pass on before the solid particles that causes 

 these molecules to rise up in the form of a wave. But we have 

 shown that they lose motion in this endeavour, and by losing it, 

 the earth loses its motion of rotation. Again, according to 

 Mayer the earth can lose its motion of rotation only when the 

 molecules of the waters, forming the tidal wave, are descending; 

 for it is only then that they can possibly be moving slower than 

 the solid parts of the earth. But, according to the explanation 

 just given, the consumption of rotation takes place also when 

 the molecules are rising. And again, according to Mayer the 

 effect cannot take place until the molecules of the water have 

 passed the point B, the meridian. According to our explana- 

 tion, the effect takes place before they reach the meridian, and 

 also at the meridian, as well as beyond it. In short, the effect 

 takes place, as we have seen, wherever the waters rise, no matter 

 where this may happen to be. The one explanation, as we have 

 already stated, is not antagonistic to the other. Both are cor- 

 rect. Mayer explains how the earth loses its motion of rotation 

 while the waters are descending to their normal level. We, on 

 the other hand, have explained how the same effect takes place 

 while the waters are rising. 



Although the lunar wave does not diminish the vis viva of the 

 earth's motion round the centre 0', we shall find, however, that the 

 same is not the case in regard to the influence of the solar wave. 

 The tidal wave produced by the influence of the sun affects, 

 although to a less extent, the earth's rotation in the same manner 

 as the wave produced by the moon. But, in addition to this, it 

 evidently exerts a retarding influence on the rotation of the 

 earth and moon on their common centre of gravity 0', and con- 

 sequently tends to accelerate the moon's mean motion. The 

 following considerations will, we doubt not, render this obvious. 



To simplify our subject, let us suppose the earth to be moving 

 round the sun, unaccompanied by the moon. In this case the 

 velocity of the earth's motion will correspond to the centripetal 

 force of the sun's attraction at the distance of the earth's centre 

 of gravity from that body. The waters on the side furthest 

 from the sun, moving in an orbit nearly 4000 miles beyond that 

 of the earth's centre, will require, in order to prevent them from 

 receding from the earth, to move slower than that centre; but 

 instead of this, they actually move swifter, being further removed 

 from the centre of rotation. The consequence is, the waters of 

 the ocean rise at this place, and constitute what we call the solar 

 wave, on the side furthest from the sun. The waters would 

 separate from the earth altogether, were it not that they are 



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