VOL. LVIII,] PHILOSOPHICAL TRANSACTIONS. 585 



-J. of the diameter of Venus, remained still obscured by the protuberance, a fine 

 stream of light flowed gently round it from each side, and completed the same 

 in the space of 3 seconds of time, from ^^ 29™ 20^ to 7'' 29"* 23* apparent time; 

 and Venus appeared wholly within the sun's lucid circumference ; but the protu- 

 berance, though diminished, was not taken away till about 20* more, when, 

 after being gradually reduced, it disappeared, and Venus's circular figure was 

 restored. 



An ingenious gentleman of his acquaintance having desired him to examine if 

 there was any protuberance of the sun's circumference about the point of the 

 internal contact, as he supposed such an appearance ought to arise from the re- 

 fraction of the sun's rays through Venus's atmosphere, if she had one; he care- 

 fvilly looked out for such a circumstance, but could see no such thing ; neither 

 could he see any ring of light round Venus, a little after she was got wholly 

 within the sun ; but he did not re-examine this latter point afterwards, when she 

 was further advanced upon the sun, at which time other persons in the obser-- 

 vatory saw such an appearance. 



How far the ring of light, which he saw round that part of Venus's circum- 

 ference which was off the sun, during the immersion, may deserve to be con- 

 sidered as an indication of an atmosphere about Venus, Mr. M. does rot at 

 present inquire; but he thinks it very probable, that the protuberance, which 

 disturbed Venus's circular figure at the internal contact, was owing to the en- 

 largement of the sun's diameter, and the contraction of that of Venus, produced 

 by the irregular refraction of the rays of light through our atmosphere, and the 

 consequent undulation of the limbs of the two planets ; the altitude of Venus 

 being only 4° 48', though the sun's limb was more distinct and steady than usual 

 at that altitude. This conjecture seems corroborated by two circumstances; one 

 is, that Venus's limb, from its first appearance to the total immersion, as well as 

 afterwards, was very ill defined, and undulated very much; the other is, that 

 her horizontal diameter, which Mr. M. measured soon after the internal con- 

 tact, with an excellent achromatic object-glass micrometer, fitted to the 2-feet 

 reflecting telescope, was only 5b\", by a mean of 8 trials, or about 3" less than 

 it should have been, from the observations made with the like instrument, at 

 the transit of Venus in 1761, by Mr. Short, Mr. Canton, Mr. Haydon, and 

 Mr. Mason, when the sun was at a considerable altitude ; and most likely the 

 sun's diameter was enlarged in proportion, though it might have been difficult to 

 have ascertained it by actual measure, had time allowed Mr. M. to make the 

 experiment with the same micrometer before the sun entered into a bLick cloud 

 uear the horizon. 



Six other persons also observed the contacts of Venus here, and noted some 

 other phenomena. Their names al-e, the Kev. Malachy Hitchins, a gentleman 



VOL. XII. 4 F 



