406 Dr. J. R. Mayer on Celestial Dynamics. 



In those actions known as the tides, such compensation^ 

 however, does not take place ; for the pressure or pull by which 

 they are produced is always stronger from east to west than 

 from west to east. The currents caused by this pull may ebb 

 and flow in different directions, but their motion predominates 

 in that which is opposed to the earth's rotation. 



The velocity of the currents caused by the tide of the atmo- 

 sphere amounts, according to Laplace's calculation, to not more 

 than 75 millimetres in a second, or nearly a geographical mile 

 in twenty-four hours ; it is clear that much more powerful 

 effects produced by the sun's heat would hide this action from 

 observation. The influence of these air-currents, however, on 

 the rotatory effect of the earth is, according to the laws of me- 

 chanics, exactly the same as it would be were the atmosphere 

 undisturbed by the sun's radiant heat. 



The combined motions of air and water are to be regarded 

 from the same point of view. If we imagine the influence of 

 the sun and that of the interior of our globe not to exist, the 

 motion of the air and ocean from east to west is still left as an 

 obstacle to the axial rotation of the earth. 



The motion of the waters of the ocean from east to west was 

 long ago verified by observation, and it is certain that the tides 

 are the most effectual of the causes to which this great westerly 

 current is to be referred. 



Besides the tidal wave, the lower air-currents moving in the 

 same direction, the trade-winds of the tropics especially, maybe 

 assigned as causes of this general movement of the waters. 

 The westerly direction of the latter, however, is not confined to 

 the region of easterly winds ; it is met with in the region of 

 perpetual calms, where it possesses a velocity of several miles 

 a day ; it is observed far away from the tropics both north and 

 south, in regions where westerly winds prevail, 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 hydro- 

 statics, 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 atmo- 

 sphere. This is the cause of the cold under current from the 

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

 equator to the poles. The waters of the latter, by virtue of the 

 greater velocity of rotation at the equator, 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 



