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102 



M A T H E M A T I C A L a nb 



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Mr. Hirft's difcernment or fidelity; as 1 am fenfible that 

 the tremors of the limbs of the Sua and Venus, occafioned 

 by the vapours at the altitude of 7% might eafily obfcure 



a faint objed. 



When Venus was a little more than half immerged in- 

 to the Sun's di(k, I fa.w her vsrhole circumference cornplet 

 cd, by means of a vivid, but narrow and ill-defined border 

 of light, which illuminated that part of her circumference 

 which was off the Sua, and would otherwile have been invi 

 fible. This I might, probably, have fecn fooner, if I had at 

 tended to it, I continued to fee it till within a few minutes of 

 the internal contad, and grew apprehenfive that it would 

 prevent the appearance of the thread of light, when it came 

 to be formed; but it difappeared about two or three mi- 

 nutes before, as well as I can remember: After which the 

 regularity of VenusV circular figure was difturbed towards 

 the place where the internal contad fhould happen, by the 

 addition of a protuberance, dark like Venus, and projed 

 ing outwards, which occupied a fpace upon the Sun's cir- 

 cumference, which bore a confiderable proportion to the 

 diameter of Venus. Fifty-two feconds before the thread 

 of light was formed, Venus's regular circumference, fup- 

 pofed to be continued as it would have been without the 



protuberance, feeined to be in contad v/ith the Sun's cir- 

 cumference, fiippofed alfo completed. Accordingly, from 

 this time, Venus's regular circumference, fuppofed defined 

 in the manner jufl: defcribed, appeared wholly within the 

 Sun's circumference; and it feemed, therefore, wonderful 

 that the thread of light fliould be lb long before it appear- 

 ed, and the protuberance appearing in its fi;ead. 



At length, when a confiderable part of the Sun's clr-. 

 eumference, equal to one third or one fourth of the dia- 

 meter of Venus, remained fill obfcurcd by the protube- 

 rance, a fine ftream of light flawed gently round it from 

 each fide, and completed the fame in the fpace of three 

 feconds of time, from y^, 29' • 2,0'' to 7''. 29' . 23'' apparent 

 time; and Venus appeared wholly v^ithin the Sun's lucid 



circumference: 



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