296 CELESTIAL DYNAMICS. 



vail, near the Cape of Good Hope, the Straits of Magellan, 

 the arctic regions, &c. 



A third cause for the production of a general motion of 

 translation of the waters of the ocean is the unequal heating 

 of the sea in different zones. According to the laws of hy- 

 drostatics, the colder water of the higher degrees of latitude 

 is compelled to flow towards the equator, and the warmer 

 water of the tropics towards the poles, in consequence of 

 which, similar movements are produced in the ocean to those 

 in the atmosphere. This is the cause of the cold under cur- 

 rent from the poles to the equator, and of the warm surface- 

 current from the equator to the poles. The waters of the lat- 

 ter, by virtue of the greater velocity of rotation at the equa- 

 tor, assume in their onward progress a direction from west to 

 east. It is a striking proof of the preponderating influence 

 of the tidal wave that, in spite of this, the motion of the 

 ocean is on the whole in an opposite direction. 



Theory and experience thus agree in the result that the 

 influence of the moon on the rotating earth causes a motion 

 of translation from east to west in both atmosphere and 

 ocean. This motion must continually diminish the rotatory 

 effect of the earth, for want of an opposite and compensating 

 influence. 



The continual pressure of the tidal wave against the axial 

 rotation of the earth may also be deduced from statical laws. 



The gravitation of the moon affects without exception all 

 parts of the globe. Let the earth be divided by the plane of 

 the meridian in which the moon happens to be into two hemi- 

 spheres, one to the east, the other to the west of this merid- 

 ian. It is clear that the moon, by its attraction of the east- 

 ern hemisphere, tends to retard the motion of the earth, and 

 by its attraction of the western hemisphere, to accelerate the 

 same rotation. 



Under certain conditions both these tendencies compensate 

 each other, and then the action of the moon on the earth's 



