82 PHILOSOPHICAL TRANSACTIONS. [aNNO 1770. 



These altitudes were taken with an English 

 quadrant of M. Sisson's make, 1 6 inches ra- 

 dius. 8' 34" are to be added to each altitude 

 to correct the error of the instrument, and 

 for the semidiameter of the wire. 

 On computing these altitudes by M. Clairaut's tables, corrected nearly by ob- 

 servations made at Paris the 30th of May and the 1st of June 1751, Mr. P. finds 

 the longitude of Cape Franqois, west of the meridian of Paris, by his own alti- 

 tudes, 4^^ 58" 8', and by those of M. de Fleurieu 4*^ 58" 20'. 



The time above noted for the total entry of Venus, is that when they perceived 

 a very slender thread of light between the limbs of the sun and Venus. They 

 judged that the limbs were in contact, but a few seconds before that instant. At 

 the exit of Venus in 1761, the limbs, being not yet in contact, and even sen- 

 sibly distant asunder, Mr. P. saw as it were a dark spot detach itself from Venus, 

 and gain the limb of the sun ; at which instant he estimated the internal con 

 tact. Many have this year seen the same phenomenon at the total entry of 

 Venus. Mr. P. was in expectation of it ; but neither he nor his associates per- 

 ceived any such thing. In I761 the sun's limbs were most exquisitely well 

 defined; in 1769 they undulated, especially at the beginning of the entry; at 

 the total entry the undulation was considerably less; and notwithstanding this 

 undulation he believes their observation a good one. On comparing the duration 

 of the transit observed at the Prince of Wales's Fort, with that of Father Hell, 

 at Wardhus, he finds on a first calculus, which he believes at least nearly exact, 

 that the sun's parallax is Q".! 1. 



Aug. 16, at St. Croix in TenerifFe, the first satellite emerged at 9*" 16" 5', 



apparent time. 



03 ijei: 



XLI. Observations of Immersions and Emersions of Jupiter" s first Satellite, made 

 at Funchal, in Madeira, with a Reflecting Telescope of 18 Inches Focus, made 

 by Mr. Short. By the late Thomas Heberden, M.D., F.R.S. p. 502. 



The time was found by taking equal altitudeSj vvith a quadrant of 12 inches 

 radius, made by Mr. Bird, and with the help of a good pendulum clock made in 

 London. And the latitude of the place of observation in Funchal, by a mean of 

 several observations made with the same quadrant = 32° 33' 35*. By comparing 

 these observations with similar ones made at Greenwich, the mean among the 

 the whole gives l*" 6" 55'.6 for the longitude of the place. 



XLII. Account of the Transit of Mercury, observed at Norriton, in Pennsyl- 

 vania, Nov. 9, 1769, agreeable to on Appointment of the American Philoso- 



