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By a. VAUGHAN, B.A. (Cantab.), B.Sc. (Loxd.). 



THIS paper deals only with the argument for solidity 

 deduced from the existence of a fortnightly ocean 

 tide, caused by the moon's attraction. 



Were the interior of the earth fluid, it is assumed that 

 sea-floor and water would rise together, and, therefore, the 

 tide be inappreciable. It seems, however, probable that the 

 tide would reach a very small value along coast lines, where 

 the waters of the ocean are held back in their motion, whilst 

 the tide in the interior would almost certainly move as 

 demanded by theory. 



It had been generally assumed, until recently, that the 

 movement of the water in the fortnightly tide might be 

 neglected, on account of the long period of oscillation, and 

 that, in calculating the height of the tide, the equilibrium 

 theory would give a very close approximation. It has, how- 

 ever, been shown by Professor Darwin, by the employment 

 of Laplace's method, that, in oceans of uniform depth, not 

 greater than 1,200 fathoms, the motion of the water has a 

 very appreciable effect, namely, a diminution equivalenti. to 

 at least halving the equilibrium value. There must also be 



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