ORBITAL MOTION OF THE EARTH. 5 



described, and are, therefore, in that orbital motion, 

 moved with the greatest velocity. 



Now, looking at Plates X. and XI. in vol. i., and the 

 remarks upon them on pages 98 to 101 of that same 

 volume, it appears obvious that, according to what 

 we have just stated, centrifugal force should tend to 

 raise a tide on that part of the moon's surface which 

 is turned away from the earth; for, in its orbital 

 motion round the earth, that side of the moon moves 

 with greater velocity than the side turned towards 

 the earth. 



163. When, however, we consider the orbital 

 motion of the earth, as shown by those same plates, 

 it appears obvious that on the surface of the earth 

 the orbital motion of the earth cannot give rise to an 

 action of centrifugal force analogous to that which 

 results from the axial rotation of the earth, and 

 which we have seen must also be brought into 

 play by the orbital motion of the moon if any fluid 

 lay on the surface of the latter : for all points of the 

 earth are, in its orbital motion, moved with the same 

 velocity. Not, as is the case in the axial rotation of 

 the earth, and in the orbital motion of the moon, 

 all swinging round the same axis; but each point 

 moving round a different centre, and all parts of 

 the earth moving evenly with the same velocity. 

 And, therefore, the orbital motion of the earth 

 cannot cause any effects analogous to those which 

 result from that action of centrifugal force which 



