66 HISTORY of the SOCIETY. 



S oes back about three degrees in every lunation, and completes 

 an entire revolution in nine years nearly. This motion, though 

 very remarkable and eafily determined, has the fame fault, in 

 refpe<5t of the prefent problem, that was afcribed to the other 

 irregularities of the moon ; for a very fmall part of it only de- 

 pends on the parallax of the fun; and of this Dr STEWART, 

 as will afterwards appear, feems not to have been perfectly 

 aware. 



THE propofitions, however, which defined the relation be- 

 tween the fun's diftance and the mean motion of the apo- 

 gee, were publifhed among the Tracts in 1761. The tranfit 

 of Venus happened in that fame year : the Aftronomers re- 

 turned, who had viewed that curious phenomenon from the 

 mod diftant ftations j and no very fatisfadlory refult was ob- 

 tained from a comparifon of their obfervations. Dr STEWART 

 then refolved to apply the principles he had already laid 

 down; and, in 1763, he publifhed his eflay on the fun's di- 

 ftance, where the computation being actually made, the paral- 

 lax of the fun was found to be no more than 6". 9. and his di- 

 ftance, of confequence, almoft 29875 femidiameters of the 

 earth*. 



A DETERMINATION of the fun's diftance, that fo far exceed- 

 ed all former eftimations of it, was received with furprife, and 

 the reafoning on which it was founded was likely to be fubjecl:- 

 ed to a fevere examination. But, even among Aftronomers, it 

 was not every one who could judge in a matter of fuch diffi- 

 cult difcuffion. Accordingly, it was not till about five years 

 after the publication of the Sun's Diftance, that there appeared 

 a pamphlet under the title of Four Proportions, intended to 

 point out certain errors in Dr STEWART'S inveftigation, 

 which had given a refult much greater than the truth. A 

 difpute in Geometry was matter of wonder to many, and 



perhaps 



* About 118,541,428 Englilh miles. 



