54 



MAT H E M A T I C A L and 



The Norrltoil obltrvations of the cclipfcs of Jupiter's firft Satellite are us follow. 



D. li. in. fee. 



1769. D. 



1769. J^d. 16, 14. 21. 10 Jj-n. if. 



ili'f/j 14, 



Vn T^>» 15- I Ini- I/- 



21, 



April 3, 14, 49- ^5 Tm. ifi. \ 



June 6 , 



10, 16. 40. hr>. ijl. 



7, 



12, J I. 14- 37 ^^'^- ?/^- 



13. 



il^^ry 5, II. 29. 27 Im. 'iji. , 





h. 



m. fee. 



10. 



2. 14 Em. i/l douhlful. 



u. 



,<y$. 13 Km. 'i/. 



Id. 



JT, 7"'; Fm. T//. 



8. 



43. ^4 .Km. %ii. 



12. 



5. I Em. \JL 



Now if we compare the corrcfponJent obfcrvatlons at 

 Philadelphia and Norriton on the i6th of February, the 



1 of May, and the yth of June 1769, 

 the difference of our meridians will be found from the 

 mean of them to be 57 fcconds of time, ^ This is farther 

 confirmed by the obfcrvations wx have made on the tran- 

 fit of Mercury over the Sun, on the 9th of November, 

 1769, which being compleatcd before thcfe iheets were 

 printed off, we have judged proper to infert. 



Apparent Time. 

 ThecxtcHKil contadt was at 

 ^ndat 



The difFcrcnce is 



h. 



va. fee. 

 36. 9 



?>s- 17 



by thenieanof 4 obfervations at Philadelphia, 

 by the mean of 3 obfervations at Norriton. 



yw^ 



i^ 



The internal contaifl was at 2. ^J. 34 by the mean of 4 obfervations at Philadelphia, 

 And at - - - 2, 36. 34 by the mean of 3 obfervations at Norriton. 



The ilifferencc is 



I. 



Therefore the mean of both thefc makes the diiferencc' 

 of our meridians ^6 feconds of time, which muft certain- 

 ly be more accurate than what is deduced from a few cor- 

 refponding obfervations of the eclipfes of Jupiter's fatel- 

 lites; both becaufe they afford 24 comparifons, all nearly 

 agreeing among themfelvcs, and becaufe thefe tranfits, in 

 the judgment of moft aftronomers, afford the befl oppor- 

 tunities of fettling the longitude of places. Hence if we 

 add ^6 feconds to the time of the Norriton obfervations of 

 the eclipfes of Jupiter's fatellites, they will be reduced to 

 the meridian of our obfcrvatory In Philadelphia, and may 

 be ufed in fixing our longitude from Greenwich, In the 

 following manner. 



/ 



The 



L^ 

 ■? 



e 



I 



£ 



^ 



1. 



L 



I 





^ / 



