8 THE TIDES. 



It is a priori an admissible suggestion that the ocean is 

 in a state of equilibrium under the moon's action, i.e. that 

 it is absolutely at rest (relatively to the moon), while the 

 earth rotates. But this would imply an apparent move- 

 ment of the whole body of water with a velocity equal and 

 opposite to that of the earth's rotation, i.e. at the equator 

 there would be an apparent current of about 1000 miles 

 per hour. As this does not correspond to the fact, the 

 hypothesis is practically inadmissible ; but when friction 

 is considered it appears theoretically inadmissible also. 

 For in this case friction would continually act in the 

 same direction, and its effect would be to make the east- 

 ward forces preponderate ; so that although the ocean 

 should be supposed at rest at first, it would ultimately be 

 dragged round by the earth. The actual form of the 

 earth, moreover, in which the equatorial ocean is inter- 

 rupted by continents, would render this equilibrium of the 

 ocean impossible. 



III. There is a constant current westward produced by 

 the moon's disturbing force. 



This occurs from two causes. First, the water in the 

 supposed equatorial canal has now taken the form of an 

 ellipse ; and, in consequence of friction, the places of 

 greatest elevation are not at B and _D, but somewhere 

 in the quadrants BA, CD. Now, the moon's tangential 

 force, hn, is, cceteris paribus, proportional to Ex the distance 

 of the particles attracted from the centre of the earth. It 

 follows that it is greater in the quadrants BA y CD, 

 than in the other two ; but in the former the force is 



