348 Astronomy. [Lecture 22. 



same time that they are attracted by the moon. 

 It is then certain that if all the particles of 

 the fluid with which the globe is covered were 

 attracted by an equal force and in a parallel 

 direction, the action of the moon would produce 

 no other effect than to move or displace the 

 whole mass of the globe and of the fluid to- 

 gether, without causing any other derangement 

 in the respective situation of their parts. 



But, according to the laws of attraction, the 

 parts of the superior hemisphere, that is, of that 

 portion which is nearest the moon, are more 

 forcibly attracted than the centre of the globe ; 

 and on the contrary, the parts of the inferior 

 hemisphere are less forcibly attracted. It follows, 

 then, that the centre of the globe being moved 

 by the action of the moon, the fluid which 

 covers the superior hemisphere, and which is 

 attracted more forcibly, must have a tendency to 

 move more than the centre, and consequently to 

 rise with a force equal to the excess of this 

 attraction above that which acts upon the centre. 

 On the contrary, the fluid which is expanded 

 over the inferior hemisphere being less attracted 

 than the centre of the globe, will have a less 

 tendency to the same point. It will of course 

 have a kind of centrifugal force, nearly equal to 

 the force which attracts that of the superior 

 hemisphere. Let us* then suppose that the 

 moon A, by the force of her attraction, draws 

 towards her the centre T to the extent of 20 



