292 CELESTIAL DYNAMICS. 



rotation of the earth on its axis, and the diminution and final 

 exhaustion thereof will be a consequence of such an action. 



The tidal wave causes a diminution of the velocity of the 

 rotation of the earth. 



This important conclusion can be proved in different ways. 



The attraction of the sun and the moon disturbs the equi- 

 librium of the moveable parts of the earth's surface, so as to 

 move the waters of the sea towards the point or meridian 

 above and below which the moon culminates. If the waters 

 could move without resistance, the elevated parts of the tidal 

 wave would exactly coincide with the moon's meridian, and 

 under such conditions no consumption of vis viva could take 

 place. In reality, however, the moving waters experience 

 resistance, in consequence of which the flow of the tidal 

 wave is delayed, and high water occurs in the open sea on 

 the average about 2J hours after the transit of the moon 

 through the meridian of the place. 



The waters of the ocean move from west and east towards 

 the meridian of the moon, and the more elevated wave is, for 

 the reason above stated, always to the east of the moon's me- 

 ridian ; hence the sea must press and flow more powerfully 

 from east to west than from west to east. The ebb and flow 

 of the tidal wave therefore consists not only in an alternate 

 rising and falling of the waters, but also in a slow progressive 

 motion from east to west. The tidal wave produces a gen- 

 eral western current in the ocean. 



This current is opposite in direction to the earth's rota- 

 tion, and therefore its friction against and collision with the 

 bed and shores of the ocean must offer everywhere resistance 

 to the axial rotation of the earth, and diminish the vis viva of 

 its motion. The earth here plays the part of a fly-wheel. 

 The moveable parts of its surface adhere, so to speak, to the 

 relatively fixed moon, and are dragged in a direction opposite 

 to that of the earth's rotation, in consequence of which, ac- 

 tion takes place between the solid and liquid parts of this fly- 



