352 Astronomy. [Lecture 22. 



water which has been raised by the moon, and 

 which turns with the earth, endeavours (if we 

 may use the expression) to preserve by its vis 

 inertias the elevation which it has acquired, 

 though in withdrawing from the moon it loses 

 somewhat of that elevation. Thus the water 

 carried forward by the motion of the earth on its 

 axis will be elevated more to the east of the moon 

 than it would have been without this motion ; yet 

 it will at the same time be less elevated than it 

 would have been directly under the moon, had 

 the earth continued immoveable. The motion of 

 the earth on its own axis, then, has in general a 

 tendency to retard the time of high water, and 

 to lessen its elevation. 



Both after the flux and reflux, the ocean con- 

 tinues some time quiescent, neither disposed to 

 rise nor fall, because the waters have a tendency 

 to preserve the state of rest and equilibrium in 

 which they are at the flood and ebb tide ; and 

 because the motion of the earth, displacing the 

 waters with relation to the moon, lessens the 

 intensity of the action of that luminary. These 

 two efforts counterbalance each other for some 

 moments. We must add also, that the attrac- 

 tion of the particles of the fluid to each other, 

 and obstacles of different kinds, which must 

 retard their motion, prevent them from passing 

 all at once from a state of flood to that of ebb. 



The moon passes above the eastern parts of 

 the globe before the western. The flood tide, 



