658 PHILOSOPHICAL TRANSACTIONS. [aNNO 176Q. 



XLVI. Observations of the Transit of Venus over the Sun, June 3, 1760. By 

 John fVinthrop, Esq., F. R. S. p. 351. 



Their apparatus having been wholly destroyed by fire, about 5 years before, 

 they had procured a new set of astronomical instruments, made by some of the 

 most eminent makers in London. A clock, by Mr. Ellicott, with the pendulum 

 of his invention, having the bob supported by levers. An astronomical qua- 

 drant, of 2 feet radius, made by Mr. Sisson; and an equal altitude instrument, 

 by Mr. Bird ; each having 3 horizontal wires in the telescope. A reflecting 

 telescope, of 4 feet focus; another of 2; and another of 1 foot; fitted with an 

 object glass micrometer, of 214- feet focus; all 3 made by the late Mr. James 

 Short. 



Mr. W. was obliged to remove the clock to another apartment, for the sake 

 of the transit, which he did on the 23d of May, when he took some equal alti- 

 tudes. By reason of an almost continual succession of cloudy weather till the 

 end of that month, he could make but few material observations afterwards for 

 regulating the clock. But the weather cleared up on the 1st of June, about 

 noon, and continued fine for several days, when many observations of that kind 

 were made. 



Observation of the Transit of Fenus. — Mr. W. chose to observe the transit 

 with the 2-feet telescope, as he supposed most of the observations in other parts 

 would be made with telescopes of that size; and he used a power that magnified 

 90 times, which gave a very distinct view of the spots then on the sun. Soon 

 after 2 o'clock, he began to look on the sun's upper limb, where the planet was 

 to enter. The first impression, he perceived, was at 2" 27"' 5P, by the clock, 

 the sun being then perfectly clear. He then rested his eye, which was pretty 

 much fatigued, to prepare it for the total ingress or interior contact. At 2'' 45"" 

 J 5', he began to be doubtful whether the internal contact was not formed; but 

 at 20' was satisfied that it was past, the sun's limb being restored to its integrity 

 in the place where it had been interrupted by the planet. During this interval of 

 near 5', there seemed to be a duskishness in the place of contact. By the fore- 

 going equal altitudes it appears, that the clock was now 2"" 13' -f- too slow. Mr. 

 W. therefore states the observation as follows : 



First visible impression of Venus on the sun 2*" 30'" 4* app. time. 



Internal contact 2 47 30. 



This time of internal contact, he thinks, cannot differ above 2' from the 

 truth, and perhaps may not differ 1'. But about 4* of Venus's diameter must 

 have entered on the sun before he perceived the impression. At 9 in the morn- 

 ing he observed the sun's diameter, in the horizontal direction, to be 1 21 1 

 parts of the micrometer, = 3l'33*.2. At 5^ 34'" 23', the sun's north limb 

 was distant from Venus's south limb 9 3 of the micrometer, = & }6".2. At 



