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dedaCes the niDtiin of the aofides to bz twice as great as 

 by the principles of the 9th feilioa. Frifius, obferving that 

 Walmfly in his method had omitted the difliirbing tangen- 

 tial force as of no eftc£l in its mean quantity, endeavours 

 to corred his folution by ufing the mean velwity of the moon in 

 odants, and her mean periodic time as afTeded by the tangential 

 force. He then finds the refult the fame as Walmfly. But upon 

 examining his method, it will be feen it does not differ effen- 

 tially from Walmfly's. Increafing the velocity, and decreafing the 

 periodic time, does not affed the angle between the apfides. The 

 motions of the apHdes in orbits little excentric, as the above and 

 next propofition flievv, almoft entirely depend upon the variation 

 of centripetal force. The variation of the force in Walmfly's and 

 Frifius's methods will, upon examination, be found to be precifely 

 the fame as Newton's, and therefore the motion of the apfides 

 ought to be the fame. The errors in the proceffes of Walmfly and 

 " Frifius are exadly alike. The fpace nfed by them for finding the 

 time is only an approximation to the excentricity. At the end of 

 the fpace the velocity is evanefcent, and from that circumftance 

 the fluent of the fluxional expreffion of the time muft be er- 

 roneous. 



Taking ^=,05 5, as in the lunar orbit, the angle between the 

 apfides will •differ about 4 feconds from the limit, confequently 



the 



