VOL. LXXVII.] PHILOSOPHICAL TRANSACTIONS. 22g 



air hereafter cited. It will be shown in the sequel, that the latitude thus found 

 does hot at all depend on the truth of the total arc, but only supposes the instru- 

 ment proportionally divided at the points answering to the pole and the equator. 

 From the whole then I conclude, that the latitude of the Hoyal Observatory at 

 Greenwich is firmly established from Dr. Bradley's observations and my own at 

 51° 28' 40', probably without the error of a single second. 



Let us now inquire into the latitude of the Royal Observatory at Paris. M. le 

 Monnier, in the JVIemoires of the Royal Academy of Sciences for 1738, and in 

 his Histoire Celeste, has examined into the latitude of the Royal Observatory at 

 Paris, resulting from the observations of the principal French astronomers, and ■ 

 assuming the refraction at the height of the pole at Paris to be 50'^ which is 2" 

 less than Dominico Cassini's table gives, and the same which Dr. Bradley's rule 

 gives, he finds the latitude of their Royal Observatory as follows : 







From the observations of M. Picard 48 



M. de la Hire 48 



Le Chev. de Louville 48 



. M. Maraldi 48 



His own observations in 1/38, after examining and making an 

 allowance for the error of the total arc of his quadrant. 48 50 14 



His further observations in 1740, making allowance for the error 

 of the total arc of his quadrant, and considering the effect of the state 

 of the air indicated by the thermometer on the refractions 48 50 15 



In the Memoires of the Royal Academy of Sciences for 1744, M. 

 Cassini de Thury (the author of the memoir) finds from his own ob- 

 servations, with the same refractions 48 50 12 



In the Memoires of 1755, the Abbe de la Caille, from a nice and 

 accurate calculation of his observations made at the College of Maza- 

 rine, at Paris, and the Cape of Good Hope, deduces new tables of re- 

 fraction suitable to each place, and states their respective latitudes, and 

 thence that of the Royal Observatory at Paris 48 50 14 



Hence the ancient observations of M. Picard, M. de la Hire, and 

 the Chevalier de Louville give 48 50 10 



The modern and more accurate observations of M. Maraldi, M. le 

 Monnier, M. Cassini de Thury, and the Abbe de la Caille, give . . . 48 SO 14 

 which is now generally made use of by the French astronomers as the true lati- 

 tude of their Royal Observatory; and, from the near agreement of so many dili- 

 gent observers and able astronomers, cannot be supposed to differ above 2 or 3'^ 

 from the truth. The difference of this and 51° 28' 40^ the latitude of the 

 Royal Observatory at Greenwich above stated, is 2° 38' 26', the true difference 



