VOL. LIII.] 



PHILOSOPHICAL TRANSACTIONS. 



7J5 



1743, 

 By the external contact at egress 



observed by myself. 

 M. De la Caille. . . . = 9*" 18^5 



Maraldi = 9 38.5 



Le Monnier. . , . = 9 23.5 

 Cassini, sen. . . . = 9 22.5 

 Cassini, jun. , . . = 9 44 5 



5 ) 47 29.5 



1753. 



By the external contact at egress 

 observed by Dr. Bevis. 



M. Cassini = 9"" 26^5 



Bouguer = 8 57-5 



Del'isle = 9 7.5 



Merville = 9 I9.5 



Libour = y 30.5 



LeGentil = 9 26.5 



De la Lande =9 25.5 



1753. 



By the internal contact at egress 

 observed by myself. 



M. Cassini =9" 22'5 



Bouguer = 8 53.5 



De I'isle = 9 3.5 



Merville = 9 15.5 



Libour = 9 26.5 



Le Gentil = 9 22.5 



De la Lande . .. = 9 21.5 



9 29.9 



M 



Mean of these 5 

 1753. 

 By the internal contact at egress 

 observed by Dr. Bevis. 



Cassini = T 25'5 



Bouguer = 9 6.5 



De I'isle = 9 5 5 



Merville . . 

 Libour .... 

 Le Gentil. . 

 De la Lande 



= 9 

 = 9 

 = 9 

 = 9 

 = 9 



1 5 

 0.5 

 9-5 

 3.5 



7) 65 13.5 



Mean of these 7 . . 9 19 



1753. 



By the internal contact at egress 



observed by myself. 



M. Cassini = 9 



Bouguer = 8 



De I'isle = 8 



Merville = 8 



Libour = 8 



LeGentil = 9 



De la Lande. . . . = s 



7 ) 64 45.5 

 Mean of these 7. . 9 15.1 



18'5 

 595 

 58.5 

 54.5 

 53.5 

 2.5 

 55', 5 



7 ) 63 52.5 



7 ) 63 3.5 



Mean of these 7. . 9 7.5 Mean of these 7. . 9 0.5 



The mean of the above 1 mean is = gm ] (5 7s 



The mean of the above 63 results of the difference of longitude be- 

 tween Greenwich and Paris is =: g 15 



The mean of 43 results which differ not more than 15* from the 



mean of the whole is = g iQ 



The mean of 19 results which differ less than 15% and more than 8* 



from the mean of the whole, is = g 14.2 



The mean of 24 results which differ less than 8* from the mean of 



the whole is = g 1 7.5 



The mean of the above 5 means is = g 15. g 



And even the mean of those 20 results which differ more than 1 5* from the 

 mean of the whole, and which are rejected, gives the said difference = g'" 12-?-' 

 which differing only 3^* from the 43 results, is a proof of the great accuracy in 

 the determination of the differences of longitudes by observations of the transit of 

 Mercury over the sun. 



Let us now examine the limit of the errors in these 1 several sets of determi- 

 nations, and we shall find that the limit of the errors in the year 

 1723 is = 27^ by the internal contact at ingress. 

 1736 is = 30 by the external contact at egress. 

 1743 is = 40* by the internal contact at egress. 



• If we reject the observations of M. le Monnier, in which there seems to be some mistake, be- 

 cause it differs considerably from the rest, the limit of the error will be = 29% agreeing nearly with 

 the other limits.— Orig. 



4 T 2 



