76 THE OCEAN. [Book III. 



earth's gravitation and that of other forces of gravita- 

 tion ; so that, as the earth's attraction tends to draw 

 the moon to the earth, those other forces tend equally 

 to draw it in the opposite direction. Then the stone 

 is drawn to the earth, but the moon is not, because 

 the stone is within the sphere in which the force of 

 attraction drawing towards the earth is greater than 

 that drawing towards the position which any other 

 force of gravitation tends to give it ; whereas the moon 

 is just so far removed from the earth as to be held in 

 equilibrium between a tendency to the position which 

 the sole action of the earth's gravitation would give 

 it if unopposed by other forces, and a tendency to 

 the position which, if the earth's force of gravitation 

 were withdrawn, the combined action of all other 

 forces of gravitation would give it. 



This, however, accounts only for the moon with- 

 standing the attraction towards the earth, whereas 

 the theory which assumes an innate tendency to 

 move uniformly forwards in a straight line accounts 

 also for the moon's onward motion in its orbit. A 

 cause for the onward motion of the moon, according 

 with the action of well-known laws, is, however, 

 indicated by the tides : for the moon tends to raise 

 a mass of water, or tide, on the earth's surface be- 

 neath it ; and, as the earth's surface rotates eastwards 

 it tends to carry that mass of water or tide with it ; 

 and therefore, as the moon tends to hold the tide 

 beneath it, the rotation of the earth eastwards must 



