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of a ring revolving round its centre, is to the momentum of the 

 fame ring revolving round one of its diameters, as tw o to one ; 

 therefore compounding thefe ratios, and ex aqiio the momentum 

 of a fphere revolving round its axis, is to the momentum of a 

 ring revolving round one of its diameters, as %p to 15 «, or as 

 800000 X quantity of matter in the fphere, to loooooo X the 

 quantity of matter in the ring. 



If therefore 9" 7" 20", viz. the quantity of the preceffion, 

 which according to Newton's calculation arifes from the adion 

 of the fun alone, be encreafed in the ratio of 925725 to 800000, 

 it will become i o' 33 . 



But it is well known, that the true quantity of the preceffion, 

 arifing from the aclion of the folar force, is nearly double this 

 quantity. Since therefore the corredion of this 3d Lemma will 

 not account for the great difference between the refult of Newton's 

 calculation and the truth, we muft look for the caufe of the 

 difference elfewhere. Simpfon is of opinion, that it arifes from 

 this, that the momentum of a very Qender ring revolving about 

 one of its diameters, is only the half of what it would be if the 

 revolution were to be performed in ,a plane, about the centime 

 of the ring ; and therefore, that all conclufions, which do not take 

 this into the account, muft be two little byjuft one half But it is 

 evident, that this cannot be the true caufe of the difference, becaufe 

 Newton did adually coniidcr, that the motion of a riog round one 



of 



