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leaves quite out of consideration the antagonist influence of the 

 centrifugal force upon the circumference of the revolving mass. 

 It is the action of the centrifugal force that makes a body, re- 

 volving in an orbit with its circumference unaffected by a pri- 

 mary's attraction, turn round on its axis from east to west, or pre- 

 serve its parallelism ; and if the function of making it rotate in 

 the contrary direction, from west to east, were to be assigned, 

 as it is by Bernouilli's hypothesis, to the same centrifugal power, 

 that power would be brought into the rather awkward predica- 

 ment of acting as its own antagonist, in producing two contrary 

 movements at the same time in the same body, and thereby neu- 

 tralizing its own efforts. The hypothesis, therefore, may be 

 fairly rejected as insufficient and untrue. 



If the earth were affected exclusively by the sun's attraction 

 of gravitation, her rotation, I believe, might be easily, simply, 

 and sufficiently accounted for in the manner I have proposed ; 

 but she does not move alone in her orbit, and, with such a com- 

 panion as the moon, the problem becomes somewhat more com- 

 plicated, though scarcely more difficult; for the moon's attrac- 

 tion acts in the same direction as the sun's, and helps to turn 

 the body round ; and not merely helps, but probably she is the 

 principal agent, her power, from her nearness, upon the earth's 

 circumference being much greater than the sun's. To this view 

 of the case there may be one objection started, namely, that the 

 liquid portion of the earth's surface moves westward, contrary to 

 the rotation, which would not happen if the moon herself were 

 the cause of the rotation. But the earth's rotation is not the ef- 

 fect of the moon's action only ; it is produced by the combined 

 operation of its own centrifugal power, the centripetal power of 

 the sun's attraction, and the moon's power ; and the effect of the 

 combined causes is to make it rotate faster than the moon re- 

 volves, so that the solid parts of the rotating mass continue to 

 move forward, while the liquid parts, more easily affected by, 

 and consequently more obedient to, the moon's power, are left be- 

 hind, to a certain extent, by the solid parts, which slip away from 

 below them. The waters of the ocean do not really move back- 

 wards, or in a direction contrary to that of the earth's rotation ; 

 they only, owing to their liquidity and greater susceptibility of 

 external affections, rotate more slowly than the solid parts ; but 

 still they do participate in the general rotatory movement, pass- 

 ing the moon every day, as well as the dry land. " What," says 

 Punch, "is the cause of the earth's rotation? Probably, because 

 one good turn deserves another" This jocular piece of philoso- 

 phy is not so far from the truth as might be imagined ; for one good 

 turn not only deserves, but really tends to produce another ; and 

 the uniformity and regularity of the earth's rotations are just the 



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