™ct. iv.] DISSERTATION SECOND. 105 



other inequalities, it does not appear that Newton attempted 

 an exact determination of them, but satisfied himself with 

 this general truth, that the principle of the sun's disturbing 

 force led to the supposition of inequalities of the same 

 kind with those actually observed, though whether of the 

 same exact quantity it must be difficult to determine. It 

 was reserved, indeed, for a more perfect state of the cal- 

 culus to explain the whole of those irregularities, and to 

 deduce their precise value from the theory of gravity. — 

 Theory has led to the knowledge of many inequalities, 

 which observation alone would have been unable to dis- 

 cover. 



While Newton was thus so successfully occupied in 

 tracing the action of gravity among those distant bodies, 

 he did not, it may be supposed, neglect the consideration 

 of its effects on the objects which are nearer us, and 

 particularly on the Figure of the Earth. We have seen 

 that, even with the limited views and imperfect informa- 

 tion which Copernicus possessed on this subject, he as- 

 cribed the round figure of the earth and of the planets to 

 the force of gravity residing in the particles of these bo- 

 dies. Newton, on the other hand, perceived that, in the 

 earth, another force was combined with gravity, and that 

 the figure resulting from that combination could not be 

 exactly spherical. The diurnal revolution of the earth, 

 he knew, must produce a centrifugal force, which would 

 act most powerfully on the parts most distant from the 

 axis. The amount of this centrifugal force is greatest at 

 the equator, and being measured by the momentary recess 

 of any point from the tangent, which was known from the 

 earth's rotation, it could be compared with the force of 

 gravity at the same place, measured in like manner by 

 the descent of a heavy body in the first moment of its 

 fall. When Newton made this comparison, he found that 



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