23 



THE POPULAR SCIENCE MONTHLY. 



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the point C, the centre of gravity between herself and the moon, is 

 only about sixty-five miles an hour; while the surface at B (Fig. 2) 



moves with a velocity of 6S,000 

 miles an hour around the sun. 

 Nevertheless, as the waters are 

 driven toward these respective 

 tangents by the effect of centrif- 

 ugal force, the tide -wave must 

 be greatest where the distance 

 between tangent and curve is the 

 n G " 3. greater. 



Let us now proceed to prove 

 by mathematical demonstration 

 the falsity of the theory of the 

 tides found in our text-books. 



Herschel, in his "Outlines of 

 Astronomy," uses the following 

 language : " That the sun, or moon, 

 should by its attractions heap up 

 the waters of the ocean under it 

 seems to them (objectors) very nat- 

 ural. That it should at the same 

 time heap them up on the oppo- 

 site side seems, on the contrary, 

 palpably absurd. The error of 

 this class of objectors .... con- 

 sists in disregarding the attraction 

 of the disturbing body on the mass 

 of the earth, and looking on it as 

 wholly effective on the superficial 

 water. Were the earth, indeed, 

 absolutely fixed, held in its place 

 by an external force, and the water 

 left free to move, no doubt the ef- 

 fect of the disturbing power would 

 be to produce a single accumula- 

 tion vertically under the disturb- 

 ing body. But it is not hj its 

 whole attration, but by the differ- 

 ence of its attractions on the su- 

 perficial water at both sides, and 

 on the central mass, that the wa- 

 ters are raised ; just as in the the- 

 ory of the moon the difference of 

 the sun's attractions on the moon 

 FlG 4. and on the earth (regarded as 



