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ASTRONOMICAL PAPERS 



103 



circumference; but the protuberance, though dlminiflied, 





was not taken away till about 20'' more, when, after be 

 ing gradually reduced, it difappeared, and Vcnus's circu- 

 lar figure was reflored. 



An ingenious gentleman of my acquaintance bavin 

 defired me to examine if there was any protuberance of 

 the Sun's circumference about the point of the internal 

 conta£l:, as he fuppofed fuch an appearance ought to arife 

 from the refradion of the Sun's rays through Venus's at- 

 mofphere, if fhe had one; I carefully looked out for fuch 

 a circumftance, but could fee no fuch thing; neither could 

 I fee any ring of light round Venus, a little after flie was 

 got wholly within the Sun: But, I confefs, I did not re- 

 examine this latter point afterwards, when flie was further 

 advanced upon the Sun, at which time other perfons at 

 the obfervatory faw fuch an appearance. 



How far from the ring of light, which 1 faw round that 

 part of Venus's circumference which was off the Sun, dur- 

 ing the immerfion, may deferve to be confidered as an in- 

 dication of an atmofphere about Venus, I Ihall not at pre- 

 fcnt inquire; but I think it very probable, that the protu- 

 berance, which difturbed Venus's circular figure at the in- 

 ternal contad, was owing to the enlargement of the dia- 

 meter of the Sun, and the contradion of that of Venus, 

 produced by the irregular refradion of the rays of light 



through our atmofphere,. and the confequcnt undulation of 

 ' the limbs of the two planets; the altitude of Venus beino- 



only 4'' 48^ though the Sun's limb was more diftindand 

 fteady than ufual at that altitude. This conjedure fecms 

 corroborated by two circumftanccs : one is, that Vcuus's 

 limb, from- its firft appearance to the total immerfion, as 



as afterwards, was very ill defined, and undulated 

 very much; the other 



well 



IS, that her horizontal diameter, 

 which I meafured foon after the internal, contad with an 

 excellent achromatic objed glafs micrometer, fitted to the 

 two feet refleding telefcope, was only fifty-five and three 

 fourths of a fecond, by a mean of eight trials, or about f 



lefs 



