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MATHEMATICAL and 



" As to the firft difturbance in the Sun's limb, it may 

 be worthy of confideration, whether it was really from the 

 interpofition of the limb of Veitusy or of her atmofphere. 

 One cannot eafily imagine it to be the former, without 

 fuppofing her limb and body much more ragged and une- 

 ven, than they appear when feen on the Sun. An atmof- 

 phere is a much more probable fuppofition,not only from 

 the faint and waterifli colour at firft, but the undulatory 

 motion above mentioned, which might arlfe from the grow- 

 ing dcnfity of the atmofphere, pufliing forward on the 

 Sun, and varying the refraction of his rays, as they pafs 



in fuccefFion through it. 



'' If fuch an atmofphere be granted, it will probably ac 

 count for the tremulous motion, in the thread of light creep 

 hvr round Venus at the internal contaB ; which may be 

 thus prevented from clofing and adhering quietly, till this 

 atmofphere (or at leaft its denfeft part) has entered wholly 

 on the Sun, and confequently the co-incidence of the limbs 

 be paft. For, though the atmofphere of Venus (as far as 

 we could poffibly judge) be not vifible on the Sun; yet that 

 part of it which is furrounding, or juft entering his limb, 

 may be vifible; having, if I may fo exprefs it, a darker 



ground behind it. 



But thcfe arc only hafty conjectures, fubmltted to 



.others; although, if they have any foundation, it would 

 make Ibme difference in the time eflimatcd between the 

 contaBs. And therefore, thofe allronomers who may happen 



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bcft to fix on fome general mode of pronouncing with re- 

 fpedlto the contacts; either by ncglefting this atmofphere 

 altogether; or taking their time from the appearance and 

 -difappearancc of its cffcds on the Sun's limb. In cither 

 cafe, it is prefumcd the times of different obfervcrs having 

 nearly the fame altitude of the Sun, and equal advantages 

 of w^eather and inftruments, would not differ fo much as 

 has been the cafe hitherto, even among eminent allrono- 

 mers at the fome place." 



General 



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