W. Dennis on the Theory of the Tides. 235 
: do not maintain their general figure and outline under the 
influence of gravity alone. On the contrary it is well known 
that by the centrifugal force generated by the earth’s rotation on 
its axis they are kept at a higher level or greater distance from 
the centre on other parts of the globe than at the poles, this ele- 
Yation amounting at the equator where it is atest to about 13 
miles, ey are therefore exactly suspended or poised between 
these two forces, namely, the force of gravity and the centrifugal 
force just mentioned, and any other force that should in the least 
degree add to or counteract the influence of either of these 
