VOL. XVII.j 



PHILOSOPHICAL TRANSACTIONS. 



453 



October. 



^pril. 



These numbers fitly represent all the observations hitherto made, nor need 

 we doubt of the future ; seeing, of all the planets, Mercury is the nearest to 

 the sun, so that it cannot in the least be intercepted by the intervention of the 

 centres of the other planets, nor sensibly disturbed by those deviations, which 

 arise from their systems, and to which the superior planets, particularly Saturn, 

 are obnoxious. I have designedly omitted the parallaxes, as very inconsiderable, 

 and which» being different in different places, could not be applied in a more 

 general calculation ; and because their quantity has not hitherto been determined, 

 but from such observations they may rather be more certainly derived. I had 

 also as little regard to Mercury's diameter, because, being extremely small, he 

 seems to adhere for a very few minutes to the limb ; for by an accurate observa- 

 tion, Oct. 28, 1077, I found that scarcely two minutes were elapsed, when he 

 entirely quitted the sun ; whence I concluded its diameter to be 11", and ac- 

 cording to the ratio of the distances from the earth at the other node, 1 34-* 

 nearly ; therefore 3i minutes are spent, while the whole planet directly pervades 

 the sun's limb ; but passing obliquely, he continues on it a little longer, in the 

 ratio of the increase of the secants of the angles of incidence. There is also 

 as little occasion to estimate the equations of time, because for many days in 

 each month they continue constant, and as it were invariable. 



