714 



PHILOSOPHICAL TRANSACTIONS. 



[anno 1763. 



__ QUI jgs Since then we have only this one transit of Venus, by which we 

 can determine this difference of longitude, we must have recourse to the transits 

 of Mercury, of which there have been 4 since the year 1723, observed at Lon- 

 don, at Greenwich, and at Paris. I have therefore extracted from the Phil. 

 Trans., and the Memoirs of the Royal Academy at Paris, the several obser- 

 vations of the 4 transits of Mercury over the sun in the years 1723, 1736, 1743, 

 and 1753. 



The observations in the year 1723 were made by Dr. Halley at Greenwich, 

 by Dr. Bradley at Wansted, and by Mr. George Graham at London, by Messrs. 

 Cassini, Maraldi, and De I'lsle at Paris. Those in the year 1736 were made by 

 Dr. Bevis at Greenwich, and by Messrs. Cassini and Maraldi at Paris. Those in 

 the year 1 743 were made by Messrs Cassini, Maraldi, Le Monnier and de la 

 Caille at Paris, and by Dr. Bevis and myself at Mr. Graham's house in frleet- 

 street, London. Those in the year 1753 were made by Messrs. Cassini, Bou- 

 guer, De I'lsle, Merville, Libour, Le Gentil, and De la Lande at Paris, and by Dr. 

 Bevis and myself in Surry-street, London. By means of these observations, Mr. S. 

 got no less than 63 determinations of the difference of longitude between the royal 

 observatories of Greenwich and Paris, and having corrected them by parallax, 

 they are as follow : 



1736. 1743. 



By the external contact at egress By the external contact at egress 



1723. 



By the internal contact at ingress 

 observed by Dr. Halley, 



M. Cassini = 9" 23* 



Del'isle = 9 14 



Del'isle = 9 14 



Maraldi = 9 



Dr. Bradley. 



De I'isle = 9 



Cassini = 9 



Maraldi = 9 



De I'isle = 9 



Mr. Graham. 



De I'isle = 8 



Cassini = 9 



Maraldi = 9 



De I'isle = 8 



12) 110 

 Mean of these 12. . 9 



23 



12 

 21 

 21 

 12 



56 



5 



5 



_56 



^2 



12 



observed by Dr. Bevis. 



M. Maraldi = 9™ 37' 



Cassini, jun = 9 44 



Cassini, sen = 9 14 



Mean of these 3 



3 ) 28 35 

 . 9 31 



observed by Dr. Bevis. 



M. De la Caille = 9"" l6*5 



Maraldi = 9 36.5 



Le Monnier = 9 23.5 



Cassini, sen. , . . = 9 '20.5 

 Cassini, jun. . . . = 9 42.5 



1743. 

 By the internal contact at egress 



observed by Dr. Bevis. 

 M. De la Caille. . . . = 9" 4'5 



Maraldi = 9 18-5 



Le Monnier. . . . = 8 53.5 

 Cassini, sen. . . . = 9 33.5 

 Cassini, jun = 9 27.5 



5) T6 17.5 

 Mean of these 5. . 9 15.5 



5)^7 

 Mean of these 5. . 

 1743. 



19.5 



9 27.9 



By the internal contact at egress 



observed by myself 

 M. De la CaiJle 



Maraldi .... 



Le Monnier, 



Cassini, sen 



Cassini, jun, 



M. Meffier 



M. Femer . . . . 

 M. de la Caille 

 M. Maraldi . . . 



Since therefore the observations of Messrs, Maraldi and de la Caille differ so much from the ob- 

 servations of the first four gentlemen (who agree very near together) it is plain that they ought to 

 be rejected ; and indeed M, de la Caille says, in a letter to Dr. Bevis, tliat the telescope he observed 

 with was a bad one, and consequently his observation not to be depended on. M. de la Lande layt 

 the same in a letter to Mr. Maskelyne, read at the Royal Society. Orig. ' 



