626 , PHILOSOPHICAL TRANSACTIONS. [aNNO 176g. 



the sun's limb near a minute sooner. At 7^ 23™ 13^ mean time, or 7'' 25™ 28'|- 

 apparent time, as reduced from sidereal time, his lordship determined the internal 

 contact, which he judged to happen when the dark penumbra, which was so 

 sensibly perceived between the limbs of the sun and planet, was lost on the 

 completion of the thread of light. His lordship observed at a small distance from 

 the observatory, by means of a stop-watch, which was let go at the instant he 

 judged the total ingress to happen, and immediately compared with the obser- 

 vatory clock. 



Mr. Bartlett, a very excellent observer, who has been constantly employed in 

 the observatory for many years, observed with a 14 feet refractor on the north 

 side of the observatory, within hearing of the clock, the seconds of which were 

 counted by Mr. Phelps, the other assistant observer. At 7*" 7™ 4' apparent time, 

 Mr. Bartlett first saw Venus on the sun; and at 7'' 23™ \&\ mean time, or 

 7*^ 25™ 26^ apparent time, he judged the ingress to happen, the telescope mag- 

 nifying near 60 times. 



Lady Macclesfield was also pleased to attend to the observation ; and at 

 7'' 25™ 16' 4^ apparent time, judgedthe second internal contact to happen, with 

 a refracting telescope of 6 feet, through which the penumbra before mentioned 

 was hardly to be distinguished. 



The sky, though free from clouds, was charged with vapour, which occasioned 

 a constant undulation of the limbs of the sun and planet ; and the wind some- 

 times blew so hard as to incommode the observers. 



On the next morning the sky was very favourable to observation, and Mr. 

 Phelps determined the eclipse of the sun to begin at IS** 32™ 45^7 mean time, 

 or IS*' 34™ 56^7 apparent time, and to end at 20*" 17™ 23'.5 mean time, or 

 2oh igm 33**8 apparent time. The Earl of Macclesfield observed the end to 

 happen 1 second later, making use of Mr. Dollond's refractor. The latitude of 

 the observatory at Shirburn Castle is 51° 39' 22", as determined by observations 

 of the pole star, at several different times ; and is 3™ 57' of time west of Green- 

 wich, and 1™ 6' to the east of Oxford, as appears by computing the difference 

 of meridians between Mr. Short's house, Shirburn Castle, and Oxford, as they 

 result from the observations of the sun's eclipse on April 1, 1764. 



Mr. H. proposed to observe the transit of Venus and the sun's eclipse in the 

 upper room of the tower of the schools, which, though the floor of it be very 

 imsteady, yet from its elevated situation afforded him the clearest view of the 

 north-west part of the horizon, and was indeed the best place for making occa- 

 sional observations in different parts of the heavens, and at different altitudes, 

 which the place then afforded. The clock, furnished with a compound pen- 

 dulum, was for some time carefully compared with another clock of the same 

 construction, which was fixed in a small observatory in the house where he 



