

52 



MATHEMATICAL and 



1- 



The foregoing nearell dlflances of their centers are de- 

 duced from the meafured diftances of their limbs, taking 

 their diameters as they are ftated above: And the paral- 

 laxes are not computed, but meafured from a projec- 

 tion of the difk of the earth asfeen from the Sua, the pro- 

 jedlion being 21 inches and an half in diameter. 



The latitude of our ofcrvatory in Philadelphia is deter- 

 mined from the obfervations of Meffrs. Mafon and Dixon 

 with the above mentioned fed;or. From a mean of thirty 

 obfervations of the paifage of fome ftars over the meridian, 

 they found the latitude of the moft fouthern point of the 



^ 





s 



city of Philadelphia to be 39^ ^6^ . 29^^2. Our obferva- 

 tory is north of this point, 26,2 feconds, and therefore it 



latitude is 39^ 56' 55">4. 



In order to determine the parallax of the Sun, from the 

 foregoing obfervations, it is neceffary that our longitude 

 from fome fixed meridian ihould be afccrtained with the 

 moft rigorous precifion. For this purpofe we have obfer^ 

 ved various eclipfes of Jupiter's fatellites, that they might 

 be compared with the correfpondent obfervations made at 

 Greenwich and elfewliere, when we are furnillxed with 



them. 



Eclipfcs of Jupiter's SA'naxrrES, obfcrvcJ ^xJPhllaJJfhm, wkli a two rcct rcllcaor. 



D. h. m. fee. 



Ap. T-I 17^?- -^p^ii %■> 14- JO. 48 Iro. ly?. Aji. T. 



o. 49- 14 I"i' ac/. 



3767. 



B. h. m. fee. 

 Ajiril 3, 7. II, ^3 Em, 2.</. 



ic, 1% Em. ly?. 



I 



1763 



May 30, 10. 

 Jure 13, y. 

 Mar. I, 



9 



April 9, 10. 



6 Kjiu 2/. 

 46. 49 irn. \Jl. 

 37. 1 Em. ill. 



May X2, 10. 33. 9 Em. id. 

 176;. J-eL 16, 14. 21. 51 Im. Ij; 



40, IS' 4^- X I"i' 2'^' 



23, 16. 16. 21 Till. 1/7. 



Aft;/-. 17, i'^. ^5. 21 Im. a«'. 



II 



l:^, TC. 15. /jO hu. ly?, 



May J, II. 30. S8 Jm. ijl. 



With a four feet reflector. 



Jime 7, 8. 44. 37 Em. %■/. 



2,2, 8. a7. 55 Em. i/;'. 



39, 10. ai. 55 Km. 1/7. 



A'lg. 23, I a, 15. 48 Em. ry/. 



-.9^/^. II, 7, 44. 41 Em. 2i/. 



Since the foregoing account has been drawn up, wc have 



J 



by 



Maikelyne,aftro 



nomcr ropl, at Greenwich. By comparing thefe with 

 the like obfervations made at Philadelphia and Norriton, we 

 arc enabled to fettle the longitudes of our obfcrvatorics. 



But 



