. s 



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MATHEMATICAL and 



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may be made at higher altitudes; otherwife the Sun's pa-- 

 rallax will not be deducible from the tranfit of Venus with 



+ 



that accuracy which has been expeded. 



The other appearances about Venus, noted by the fix 

 obfervers, which they have communicated to me are as 

 follows : 



Pvlr. Hitchins remarks, that, at the firft contact, though 

 there was a tremulous motion in the Sun's limb, yet that 

 part of it which the planet entered was very well defined, 

 and the firfl impreflion of Venus appeared to be inftantane- 

 ous, and as a black, fliarp point. At the internal coincidence 

 of circumferences, the fluduation of the Sun's limb was 

 increafed,and the limb of Venus being afFedcd in like man- 

 ner, there was an uncertainty of about lo'^ in eftimatin 

 the faid coincidence; but at the breaking in of the thread 

 of light between the limbs, there was not a greater uncer- 

 tainty than a fecond and a half of time. At the internal 

 coincidence of circumferences, the limb of Venus next to 

 that of the Sun being protuberant, her vertical diameter 

 appeared to be longer than the horizontal one; but when 

 the Sun approached the horizon, and was fcarce above a de- 

 gree high, Venus^s horizontal diameter appeared to be fen- 

 fibly longer than the vertical, which was, probably, owing 

 to refraction. After the internal, conta£t, there appeared 

 a luminous ring round the body of Venus, about the thick- 

 nefs of half her femidiameter; it was brighteft towards 

 Venus's body, and gradually dimlnifhcd in fplendor at 

 greater diflances, but the whole was exccffive white and 

 faint. This radiancy round the planet feemed to him to 

 be greater in Mr. Nairne's two feet tclefcope than in the 

 fix feet Newtonian refledtor. 



After the fecond or internal contact, Mr. Hirft left off 

 obferving with Mr, Dunn's two feet refledlor, and had a 

 fight of Venus in the fix feet Newtonian refledor, in which 

 he thought he preccivcd a glimmering of light about the 

 upper part of the circumference of Venus, or that part of 

 the planet which enterjcd laft into the folar difk. 



After 



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