VOL. LVIII.3 PJIILOSOPHICAL TRANSACTIONS. 587 



perior to them all ; and to its greater excellence and distinctness he principally 

 attributes the difference of 26* by which Mr. Hitchins saw the internal contact 

 before him; as he can depend on his observations. Possibly the greatness of 

 the differences might arise from the low altitude of the sun and Venus; and then 

 the like difi^erences would not be so much to be feared in places where the ob- 

 servation may be made at higher altitudes; otherwise the sun's parallax will not 

 be deducible from the transit of Venus with that accuracy which has been ex- 

 pected. 



The other appearances about Venus, noted by the 6 observers, which they 

 communicated to Mr. M., are as follows : Mr, Hitchins remarks, that at the 

 first 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 first impression 

 of Venus appeared to be instantaneous, and as a black, sharp point. At the in- 

 ternal coincidence of circumferences, the fluctuation of the sun's limb was in- 

 creased, and the limb of Venus being affected in like manner, there was an 

 uncertainty of about 10* in estimating the said coincidence ; but at the breaking 

 in of the thread of light between the limbs, there was not a greater uncertainty 

 than a second 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 diame- 

 ter appeared to be longer than the horizontal one; but when the sun approached 

 the horizon, and was scarcely above a degree high, Venus's horizontal diameter 

 appeared to be sensibly longer than the vertical, which was probably owing to 

 refraction. After the internal contact, there appeared a luminous ring round 

 the body of Venus, about the thickness of half her semidiameter ; it was bright- 

 est towards Venus's body, and gradually diminished in splendor at greater 

 distances, but the whole was excessively white and faint. This radiancy round 

 the planet seemed to him to be greater in Mr. Nairne's 2-feet telescope than in 

 the 6-feet Newtonian reflector. 



After the 2d or internal contact, Mr. Hirst left oflT observing with Mr. Dunn's 

 2-feet reflector, and had a sight of Venus in the 6-feet Newtonian reflector in 

 which he thought he perceived a glimmering of light about the upper part of 

 the circumference of Venus, or that part of the planet which entered last into 

 the solar disk. After Venus was got within the sun's disk, alight a little weaker 

 than that of the sun, of a purplish colour, appeared to Mr. Horsley, to the left 

 hand of Venus, which is really to the right, the telescope inverting objects. 

 This light he saw for 6 or 7 minutes. From 7^ 28™ 26' to 7^ 28"* 30* apparent 

 time, Mr. Dunn saw a very faint rim of light at Venus's exterior limb. After 

 Venus was wholly on the sun, he saw a faint ring of light surrounding her, both 

 with the 3^feet telescope, and Mr. Nairne's 2 feet reflector. 



When -^ of Venus's diameter was entered on the sun, Mr. Dollond first saw a 

 V 4 F 2 



