4 ORBITAL MOTION OF THE MOON. 



cause an accumulation of water in the equatorial 

 regions, then, looking at the actual motion of the 

 moon in its orbit round the earth, analogy leads us 

 to infer that if on the surface of the moon there lay 

 any considerable extent of water, then not only 

 would there be, by the earth's power of gravitation, 

 a tide raised on that part of the moon's surface 

 turned towards the earth; but also even without 

 taking into consideration any possible nature of the 

 force which counteracts the earth's attraction there 

 would be, by centrifugal force, a tide raised on the 

 side of the moon remote from the earth. And this 

 accumulation of water on the side of the moon 

 remote from the earth would result from the action 

 of centrifugal force in a manner precisely analogous 

 to the manner in which the action of that force 

 causes an accumulation of water about the equatorial 

 regions of the earth. For, as in the axial rotation 

 of the earth, the velocity of the different parts of the 

 earth's surface are in proportion with the distance of 

 the different parts of the surface from the axis of 

 rotation, and centrifugal force tends to carry the 

 water to those parts of the surface which, being most 

 remote from the axis of rotation, move with the 

 greatest velocity : so also would centrifugal force 

 tend to carry any water on the surface of the moon 

 towards those parts of the moon's surface which, in 

 the orbital motion of the moon, are most remote 

 from the axis round which the moon's orbit is 



