ASTRONOMICAL PAPERS. 



47 



" When Venus had advanced with a little more than 

 half her body on the Sun, her whole eaftern Timb appeared 

 faintly illumniated: This light feemed to encreafe as fhe 

 advanced farther on the Sun, till near the time of the in- 

 ternal contad:. By this time I was convinced that Venus 

 isfurroundedbyadenfeatmofphereofa confiderable height, 

 which doubtlefs had prevented my fixing the external con- 

 ta<3:, with that accuracy I hadexpeded, and had occafion- 

 ed that inequality in the darknefsj which I had obferved. 

 on the Sun'^s limk. 



" In determining the internal contad:, which I appre- 

 hend was done with great exadnefs, I attended to the in- 

 ftant, when there was a prefed coincidence of the limb of 

 Venus with the limb of the Sun, as when two circles touch 

 internally. This appeared at 2^. 31^. 24'' apparent time.- 

 I expeded by the time the affiftant had counted another 

 fecond, to have feen light diftindly round the eaftern limb 

 of Venus; not fuch a radiance as had for 7 or 8 minutes 

 rendered that part of the planet vifible; but a certain nar^ 

 row portion of the Sun's limb which had a very diftin- 



guiflnable appearance from the light I have mentionedi 

 The edge of the Sun did not appear fo foon; neverthelefs I 

 fixed upon. 2\.3i'. 25'' for theprecife time of the internal 

 contad, being certain, that no part of Venus was then off 

 the Sum One or twofeconds more were counted before the 

 Sun appeared diftindly without the limb of Venus. But 

 then it was obvious that Venus did not then touch the Sun's 

 limib in any part, fo that the contad was certainly over." 



Mr. Prior made his obfervations with his own refled- 

 ing telefcope, whofe magnifying power he does not ccr^ 

 tainly know, but fuppofes it to be at leaft an hundred times. . 

 He gave the following account of his obfervation of the - 

 contads, viz. 



" The uncertainty where Venus would touch the Sun's 

 limb made me take the following method. From 8 or 9 

 minutes paO. two o'clock I made it a rule to pafs my eye 

 from the lower edge of the field of my tclefcope to the up- 



per, 



