J56 PHILOSOPHICAL TRANSACTIONS. [aNNO 1764. 



XLIX. and L. Observation of the Transit of Venus, June 6, I761, at St. Johris, 

 Newfoundland. By Mr. John Winthrop, Professor of Mathematics and Philo- 

 sophy at Cambridge, New England. In a Letter to J. Short, F.R.S. p. 279. 

 Having properly prepared the clock, and the astronomical instruments, they 

 waited for the critical hour, which proved favourable to their wishes. The morn- 

 ing was serene and calm. The sun rose behind a cloud that lay along the ho- 

 rizon, but soon got above it ; and at 4^ 1 8™ they had the pleasure of seeing 

 Venus on the sun ; though dimly indeed at first. But the planet presently be- 

 came distinct, and her limb well defined. Upon this, Mr. W. applied himself 

 to observe the passage of the sun's and Venus's preceding limbs, by the vertical, 

 and of their lower limbs by the horizontal wires, in the reflector, and made the 

 following observations; one of his assistants counting the clock, and the other 

 writing down the observations as he made them ; which, having made the proper 

 correction of the time for the change of the sun's declination, stand as follow : 



True time. dift". long. & $ ? lat. s. 



At 4" '2l"° 2(»' Sun at the vertical ' " 10' 47" 



21 31 Venus at the same 9 2 



23 6 Venus at the horizontal 9 4 . 10 50 



24 23 Sun at the same 



27 29 Venus at the horizontal 9 25 10 52 



28 47 Sun at the same 



35 15 Sun at the vertical 10 55 



35 2 1 Venus at the same 9 56 



37 49 Venus at the horizontal 10 8 11 00 



39 9 Sun at the same 



As Venus began now to draw near the sun's limb, Mr. W. prepared to observe 

 her egress. The interior contact did not appear so perfectly instantaneous, as 

 Dr. Halley's papers led him to expect. He was not certain of it till 4^ 47"^ 21', 

 though he doubted of it at 1 7^ The exterior contact he judged to be at 3'' 5"" 

 49', doubtful also 3 or 4'; and so the passage of Venus's diameter, IS"* 28'. ;,, 



The above observations gave him several altitudes and azimuths of Venus, 

 whence he deduced her right ascensions and declinations ; and from them, her 

 longitudes and latitudes. The result of the whole, or the planet's difl^erence in 

 longitude from the sun's centre and her latitude, is set down above, against each 

 observation of Venus. Hence he concluded that at the ceptral emersion, which 

 he put at 4'' 46™ 38% the difference of longitude was U' IQ', and the latitude 

 1 1^ 6". Also, that the conjunction in longitude happened at 2^ 4"* 36', the 

 planet's latitude then being 9' 28". 



In these calculations, he supposed the semidiameter of the sun to be 1 5' 50*, 

 and of Venus 29". 



By several observations, he found the latitude of the place 47° 3i'n; which 

 falls within the latitudes laid down in several books and maps, which make it 



