50 FORCES WHICH DETERMINE THE 



be greater than its axial diameter. The action of this 

 force would not tend to cause any difference between 

 the hemispheres lying on either side of the equator; 

 but, as far as its action is concerned, those hemi- 

 spheres would be equal and their configuration 

 similar. 



192. Let there, however, be induced, besides this 

 axial rotation, a motion onwards through space in the 

 direction of either of the poles say the south pole. 

 And, in the same manner as that in which the cen- 

 trifugal force, just above described, is concomitant 

 with axial rotation, let the magnetic action, described 

 on page 69 of volume i., be concomitant with that 

 motion through space. Then in the central line of 

 motion the surface of the earth is drawn in the 

 direction of that motion with greater force than 

 those parts of the surface remote from that central 

 line of motion, so that these latter parts have a 

 relative tendency to fall back in the opposite direc- 

 tion : and by this action, therefore, the surface of the 

 earth about the north pole is drawn inwards; that 

 about the south pole bulged outwards; that in the 

 temperate zone of the southern hemisphere pressed 

 inwards; and that in the temperate zone of the 

 northern hemisphere bulged outwards. 



193. The independent action of each one of these 

 forces is illustrated by the curve lines in the design 

 on the cover of this volume. In that design, the 

 sphere shows the action of gravitation; the oblate 



