54 PHILOSOPHICAL TRANSACTIONS. [aNNO 1763. 



sun at q!^ 42"* 26' apparent time at Greenwich. Mr. Bradley observed the same 

 at i*" 42™ 38', at Wansted in Essex (10* to the east of Greenwich) or at 1^ 42"" 

 28' when reduced to the meridian of Greenwich." Mr. Graham in Fleet-street 

 observed the same at 2*" 42™ 19*, or at 2*^ 42™ 44', when reduced to Greenwich. 

 The mean of these is 2^ 42™ 32'.7. In the observatory at Paris M. Maraldi ob- 

 served the same at 2^ 51™ 48^ apparent time ; and M. Delis le at 2*' 51™ 37% 

 but suspects it might have been some few seconds later. Mr. H. supposes it to 

 have happened at 2*' 51™ 43^5. The difference of meridians therefore is 9™ \&.S. 

 If we take a mean of Dr. Halley's and Mr. Bradley's observations only, the differ- 

 ence of meridians is 9™ l6'.5. 



In 1736, Dr. Bevis observed the last contacts of the limbs of Mercury and the 

 sun at O*" 8™ 33' at Greenwich. The same was observed at Paris by M. Maraldi 

 and M. Cassini de Thury, and at Thury by M. Cassini, at O*' 18™ 5'.5 by a mean 

 of the 3 observations. The difference of longitude therefore is 9™ 32'.5. In 

 1743, the last internal contact of the limbs was observed by Mr. Graham, in 

 Fleet-street, at l*" O™ 42% and by Dr. Bevis at Beaufort-Buildings, in the Strand, 

 at 1** O™ 33' ; or by a mean of both, when reduced to the meridian of Green- 

 wich, at l"" 1™ 04'. — ^The same was observed by the Abbe de la Caille, Mess, 

 Maraldi, Monnier, and Cassini the son, at Paris, and by M. Cassini at Thury ; 

 which observations when reduced to the meridian oi the Royal Observatory, give 

 jhjQtn i5».5 for the time of the internal contact; the difference of meridians is 



therefore 9™ 12". 5. By a mean of the observations of Mr. Graham and Dr. 



Bevis, when reduced to Greenwich, the last external contact on the same day 

 happened at l*" 2™ 42' ; and by a mean of the observations in France, the same 

 happened there at 1*" 12™ 10'. The difference of longitude therefore is 9™ 28'. 



In 1753 was another transit of Mercury, when the unfavourable state of the 

 heavens, a few seconds before the time of the internal contact, prevented any 

 observations from being made at Greenwich, as appears from a paper communicated 

 to Mr. H. by the executors of the late Dr. Bradley. Both contacts however 

 were luckily very well observed by Mr. Short, Dr. Bevis, and Mr. Bird ; by a 

 mean of whose observations, reduced to the meridian of Greenwich, the internal 

 contact happened at 10*^ 9" 37^5. The same contact was observed by 13 ob- 

 servers at Paris, and was found not to happen sooner than 10*" 18™ 36% nor later 

 than 10'' 19™ 3'. But by a mean of all, at 10'' 18*" 45'. The difference of me- 

 ridians therefore is 9" 7'.5. By a mean of the observations of Mr. Short, Dr. 

 Bevis, Mr. Bird, Mr. Canton, and Mr. Sisson, all reduced to the meridians of 

 Greenwich, the external contact happened at lO*" 12"" 17^5 ; and at the Royal 

 Observatory, by a mean of all the observations at Paris, at 10'' 21™ 33'. The 

 difference of longitude therefore is 9™ 15'.5. And if we take a mean of these 7 

 results, the Royal observatory at Paris will be found to be 9™ 17'-r to the east of 



