MATHEMATICAL akb 



But fhould theobferved* times of thofe ecllpfcs, come 

 out different at Greenwich from their calculated times in 

 the nautical almanac, for the prefent year, a corredion of 

 the difference of longitude mufl be made accordingly.. 



OBSERVATIONS /£.r/;c% t^jeUithudc e/Norriton Obfervatory, iviiUfan AJronmUaU^^ua- 



drant of t-wo and an half fed radius ; made by Siffon. "^ 



.1'hls Quadrant was fent up by Mr. Luhens, and erc(5led in the meridian of the Obfervatory 

 May 20th, by Mr. RiUcnhoufe, who took the following obfcrvatlons with it, -ulz. , 



Zenith diftances of ftars, for difcovering whether there might be any error in the inarumcnts. 



With the face of the Quadrant weflwards. 



Higheft flar in left 

 leg of Bootes 



Ar(5l'uru5 



Bright ftar in ihz 

 Crown 



20 



so. 

 ao. 

 19. 

 19. 

 19; 

 19. 



12. 



° 36'. 



O 



36. o 



46. 18 



46. 14 



46. 30 



46. %% 



39- l<> 



59' 217 



With the face eaftwards. 



I'liehefl Aar in the 

 left leg of Bootes 



ArtSlurus 



Bright flar in the 

 Crown 



o 



ao"- 3J'. Ji" 



»o- 35- J4 

 20. 2>^. 



46. 

 46. 



o 



5 

 8 



19. 



19. 

 19. 

 19. 



12. 39- 34 

 12. 39 



46. n 

 46. II 



iS 



From a mean of the above 18 obfcrvations, the error of the quadrant is 3/^5 to hcfubflraSIaf 

 from the Zenith diftancc when the face is wcilwards and added when it is eaftwards. 



OBSIiRVATlONS 



■ JMBlJ- 



* Since drawmg up the above, the Rcvd. Mr. Ma£kelync, AflronomcrRbyal, agreeable t© 

 rny requeft, hath been pleafed to communicate the following lift of eclipfcs of Jupiter's lit Sa- 

 tellite as obferved at the Royal Obfervatory, from April to June, bcth inclufive, viz, 

 J 769. Apparent time. Immerfionsof lil Sat. at Greenwich. 



D. 



March %f) 

 April 12 



28 



May 

 ,*fune 



J^h 



16 



8 

 15 



h. m. fee. 



13. %$• 1 



xL 16. 8 



14. ^s- ri 



Jimerfions. 



32- 15 



3^- 3J 

 9. 40. s(> 



3ET. 2,5- 33 



9- 50- 24 



-With 2 f. Rcflca. made by 5W/; Apert. 4,5 inches diameter, 

 with 2f. Reflea. madcby j^/n/; Apcrt. 3,>8 inches diameter, 



Wilh .S'/joH's '2 f. Rcfleaor. 



with 5/^&r/'j: 2 1. Rellctftor. 



with 6 f. N;;wtonian Reileiflor; Aperture 9 inches diameter, 

 with 6 f. ditto. 



with Short^s 2 f. Rcfledor. 

 with ditto. 



There are only three of the above cclipfes obferved at Greenwich, (viz. the % immerfions) 

 that could have been fcen here, and but one of them happens to be among thofc aduuUy ob- 



ferved, viz. 



Aprdl%tb. ^^^ ^^ 



%'^ at Green'zvkh, 



Z7 at Norriioiu 



Hence 



I. 31 



DiiTerence of longitude. 

 'Till we have an opportunity, the eniuing fpring, to obferve more cclipfes of Jupiter's Sa- 

 tellites, wc would rather depend on the difference of longitude deduced from the twp forcgoinjr 

 correfponding obfcrvations, than on the w('a« deduced from the calculated times; which, how- 

 ever, puts us only f more weft. The immcrfion of April J2tb was talun at Green-wkh with 



■wich to agree with our tckfcope, which would make ^h. V %f or 34" diff. long, the fame ; 

 got from thitrncan of the calculated times, • " • ' 



The cclipfes of 2d and 3d fatellite arc not fet down, as they are not fo much to be depended 



y 



eh, a» thole of the ift. 



