654 PHILOSOPHICAL TRANSACTIONS. [aNNO I769. 



By Doctor Wilson, External contact at g* 54"> 31 .4 



Venus's centre judged to be on the limb 7 1 33 .4 



Sun's light appeared between Venus and the limb 7 1 1 56 .7 



The beginning of the solar eclipse next morning, observed by 



Short's 18 inch reflector 18 30 14 .2 



Middle, from a series of observations with the object glass mi- 

 crometer, fitted to a 9 inch reflector of Short's 19 18 47 .7 



End not visible 



R T) WU'am on") External contact at 6" 54 28 



^ j'rv D -J /Internal contact, ■ or when the sun's light appeared between 



andDr.Reid. / Venus and the limb ^ . . .T 7 12 24 



Venus's centre judged to be on the limb, by Dr. Reid 7 I 24 



Dr. Reid marked the time when he conceived the internal contact would have 

 happened, if the dark protuberance on Venus had been taken away, and her 

 disk reduced to a circle, viz. 7'' 10" 24*. 



According to Mr. P. Wilson, external contact 6^ 54" 28' internal contact 

 7h 12" 24'. 



This gentleman remarked that his first observation should be considered as 

 only a posterior confirmation of Dr. Williamson's and Dr. Reid's external con- 

 tact ; the fact was, that when these gentlemen perceived the first contact, their 

 keenness made them call out, and it was not till then that he saw the pheno- 

 menon with perfect certainty. He was conscious however, that he fluctuated 

 concerning the reality of the appearance for about 12 seconds before that time, 

 during which his determinations were suspended, through an apprehension of 

 anticipating the real time, which was heightened by so close a neighbourhood 

 with the other observers, all of whom he could not help being sensible were still 

 expecting the phenomenon. On the whole, he was rather of opinion that he 

 would have set down the external contact at least 8 seconds sooner had he been 

 observing apart. His 2d observation, by which he means the instant when the 

 interval between Venus and the sun's limb first appeared obvious, was taken down 

 without the least knowledge of what was passing among the other gentlemen 

 who observed. 



Dr. Irvine made the external contact 3 seconds sooner than the rest ; but his 

 internal contact was some seconds later. Mr. Anderson, f. r. s. fitted up a 

 clock and apparatus in the college steeple ; his clock was regulated as above, by 

 signals from the observatory ; he observed the transit with a large reflector, and 

 his assistants observed with refractors ; they were all of them uncertain about the 

 external contact, owing to the state of the atmosphere, and *a tremor given to 

 the steeple by the wind ; but none of their other observations varied, above 3 

 seconds, from Dr. W.'s, as related above. 



Latitude of the observatory 55° 51' 32". Longitude by corresponding obser- 

 vations 0° 17' 11" of time from Greenwich west. 



