CnAP. XXI. J THE HEAVENS. 257 



resists this horizontal motion exactly as that at the 

 point a resists the downward motion ; and the tan- 

 gential action of the force at h also supports the top ; 

 because it tends to carry the point h farther than the 

 point d, from the centre x, just as the tangential 

 action at the point a makes the top revolve by tending 

 to carry the point a farther than the point c from the 

 centre x. 



If the velocity of rotation be great, the force at b 

 will lift the top into an upright position m the same 

 manner as the force at a carries the top round in the 

 direction e f g h. 



As soon as the velocity with which the top rotates 

 becomes so slow that it falls, under the influence of 

 the earth's gravitation, the onward motion commu- 

 nicated to it by the action of astral gravitation is 

 immediately reversed, and it runs on the ground like 

 a wheel. 



PROPOSITION XXVII. 



Problem. — To apply Proposition XX V. to the up- 

 heaval of the ocean round the equatorial regions 

 by the action of the earth's rotation and to its 

 constant circulation in that position. 



1. Let the cu-cle n w s e (Fig. 22) be the 

 surface of the earth, n the north, and s the south 



s 



