726 PHILOSOPHICAL TRANSACTIONS. [aNNO 1745. 



Presently after the sun was covered with clouds. About 10 the clouds opened 

 for a moment, when Mercury was seen on the sun. About noon it began to 

 clear up, when Dr. B. renewed his application, and made the following obser- 

 vations. 



Oct. 30^ 13^ 50" 45*App. time, the centre of Mercury was l' 18'' distant 



from the sun's nearest limb, by the micrometer. 

 31 O 2 39 Mercury was about his own diameter distant from the 

 sun's limb. 



7 4 the centre just emerged. 



8 33 the exterior contact, the sky being very clear. 



The diameter of Mercury was so small, that with the microscope it hardly 

 measured 10 seconds. 



The transit of Oct. 25, 1743, he observed at Beaufort-buildings, situated 

 about half a minute of time west from the Royal Observatory. Mr. Sisson 

 counted the clock, while Dr. B. observed the sun. 



At 8 in the morning nothing appeared on the sun, and he was soon after ob- 

 scured by clouds. At 10-^*^ he first saw the planet on the sun, the transit being 

 then nearly finished. About noon the sky cleared up again, and allowed the 

 Dr. to make the following observations. 



Oct. 25"^ O** 58*" 34' app. time, the distance of their limbs was nearly equal 



to Mercury's diameter. 

 1 O 33 the last interior contact. 



1 25 thecentre just emerged. 



2 l6 the last exterior contact. 



The day before, a little after noon, he took the sun's diameter, equal 

 to 32' 27". 



Mr. Bird made a good observation, near the beginning of the transit, in 

 Surrey-street, about l-f minute of time east of the Doctor's situation. He 

 perceived a very small thread of light between the sun and Mercury, which had 

 just entered, scarcely equalling a lOth of the planet's diameter, at 8'' 30™ 56% 

 that is, at 8*^ 30*" 544-' at Beaufort-buildings. Hence, Dr. B. infers the total 

 ingress at his situation to 8^ 30™ 40^ as nearly as possible 



He therefore sets down the whole transit, as seen at Beaufort-buildings, as 

 follows : 



Oct. 24'' 20*' 28"° 57' app. time, the first exterior contact. 



the ingressus of the centre, 

 the first interior contact. 

 Oct. 25 1 O 33 the last interior contact. 



the egressus of the centre, 

 the last exterior contact. 



