650 



PHILOSOPHICAL TRANSACTIONS. 



[anno 1769. 



General table of the contacts of the limbs of the sun and Venus, as observed 

 at Norriton, June 3, 1769, reduced to apparent time. 



June 3, by the before-mentioned tables of the work, the sun's centre was on 

 the meridian, at ll''58'"49' by the clock, and June 4, at ll''59™2", and 

 therefore gained IS'' in 24 hours of apparent time. Therefore at noon June 3, 

 the clock being 1™ 1 r slow of apparent time, it was only 1" 10' slow at the 

 observation of the contacts. Whence 



The apparent time of the different contacts was : 



External contact, by Dr. Smith. 



1 St visible impression on ^j h m s s 



the sun's limb, in form / 

 of a quivering dusky >2 12 50 to 53 

 shadow, with many I Uncertain to 3* 



points J or 4' 



A well defined black I 



dent in the sun's limb, > 2 13 15 



at J 



Extern, contact, by Mr. Lukens. 



External contact, 



by Mr. Rittenhouse. 



Judged of as 1 h m s 



I described in >2 12 49 



; his account J 



Internal contact. 

 Judged from a thread ^ 

 or crescent of light, / 

 closing round the dark > 2 30 15 

 body of Venus, with a I 

 tremulous motion, at J 



h m « 

 A small dent 1 

 in the sun's \ 2 13 13 

 limb . . 



ti's V ; 



Internal contact. 



2 30 8 to 14 



internal contact. 



2 29 55 



When Venus was fully entered on the sun's limb, and the gentlemen had 

 satisfied themselves by comparing their different notes of the contacts, which were 

 thrown together on the table of the observatory, they prepared for the micro- 

 meter, and other observations. The greatest part of the micrometer obser- 

 vations were taken by Dr. Smith, while Mr. Rittenhouse undertook to take 

 another set of observations ; namely, the appulses of the limbs of the sun, and 

 the centre of Venus, to the cross hairs of the equal altitude telescope ; Mr. 

 Lukens taking and writing down the time for him. 



From a mean of the observed 6' diameters of Venus on the sun, allowing for the error of adjust- 

 ment, as mentioned below : 



Venus's diameter, for the day of the transit, was 0* b7".i 



The sun's semidiameter, from a mean of 5 horizontal diameters, taken the same day 15 47-0 



Or, from a mean of 4, taken that day, leaving out the second, which Mr. Lukens 



thinks he may have taken too large 15 45.0 



All the micrometer observations were separately reduced to their value in minutes and seconds, 

 both by Mr. Rittenhouse and Dr. S. Many more might have been taken ; but as so many persons 

 were desiious of looking through the telescope, they could not well be denied ; and the number 

 above set d(>wn are found fully sufficient for all the purposes of the projection ; especially as they 

 have been found to agree so well with each other. 



The observations being thus finished, Mr. Rittenhouse was pleased to under- 

 take the projection of the transit from them ; which he delineated in an exact 

 manner. 



i 



