154 POPULAR LECTURES AND ADDRESSES. 



now attempt to speak of it sufficiently to allow us 

 to have it as a foundation for estimating the forces 

 with which we are concerned, in dealing with some 

 of the very perplexing questions which tidal 

 phenomena present. 



We are to imagine the moon as attracting the 

 earth, subject to the forces that the different bodies 

 exert upon each other. We are not to take Hegel's 

 theory that the Earth and the Planets do not 

 move like stones, but move along like blessed gods, 

 each an independent being. If Hegel had any 

 grain of philosophy in his ideas of the solar system, 

 Newton is all wrong in his theory of the tides. 

 Newton considered the attraction of the sun upon 

 the earth and the moon, of the earth upon the 

 moon, and the mutual attractions of different parts 

 of the earth ; and left it for Cavendish to complete 

 the discovery of gravitation, by exhibiting the 

 mutual attraction of two pieces of lead in his 

 balance. Tidal theory is one strong link in the 

 grand philosophic chain of the Newtonian theory 

 of gravitation. In explaining the tide-generating 

 force we are brought face to face with some of the 



