TRANSLATOR'S INTRODUCTION xlv 



view, however, even if it had been well founded, 

 would not entirely or necessarily disprove his earlier 

 solution ; it would only complicate the calculation of 

 the amount of the tidal retardation. But Kant does 

 not recur to his former view, nor even mention it. 

 Euler's theory, however, falls with the abandonment 

 of the old hypothesis of the molten state of the 

 internal mass of the earth, and the acceptance of 

 the new view of its practically perfect rigidity as 

 maintained by Lord Kelvin. 1 Kant's original dis- 

 covery thus remains unaffected, and is now almost 

 universally accepted. 2 



(5) The most important application which Kant 

 made of his great discovery was to the explanation of 

 the past retardation of the rotation of the Moon 

 round its axis, until it has come to correspond to its 

 monthly period of revolution around the Earth, and 

 to the anticipation of the retardation of the rotation 

 of the Earth, until it shall come to be equal to the 

 monthly revolution of the Moon around it. The 

 Earth will then turn always the same face to the 

 Moon, just as the Moon now does to the Earth, 

 and the Moon shall then appear to it as standing 

 always on the same meridian, on account of the 



1 W. Thomson (Lord Kelvin) 'On the Rigidity of the Earth' in the 

 Transactions of Roy. Soc., May, 1863; and Treatise on Natural 

 Philosophy, I., 422. 



2 But v. Kirchmann, strangely^ still opposes Kant's view, on the 

 ground that the tidal wave is only a vertical rising and falling of the 

 water of the ocean (Erlauterungen, Phil. Bib., 63)* Surely he can 

 never have seen a tide breaking on a shore. 



