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ASTRONOMICAL PAPERS. 



7 



2 



32 27"; the total effe6t of thefe parallaxes to accele- 

 rate the internal contad being 4' 4". 



Thefe times depend upon the longitude of Philadelphia, 

 weft of Greenwich, which in this calculation is fuppofed to be 

 5\ o' 32", whichisasnear aslhaveyet beenable toafcertain 

 It, by comparing a number of obfcrvations made on the e- 

 clipfes of the firft fatellite of Jupiter, with Mr. Emmerfon*s 

 tables. But thefe cannot be depended upon for the longi- 

 tude, within a minute or two of time, which will by no 

 means anfwer the dcfign of afcertaining the diftances of 

 the Sun and planets by the enfuing tranfit. I would there- 

 fore beg leave to propofe to the Society, that provifion be 

 made, without lofs of time, for ereding a fmall obfervatory 

 in fome convenient place that the occultations of fomc 

 known ftars by the Moon, and the eclipfes of Jupiter^s fa- 

 tellites, rnay be noted, and compared with the correijion- 

 ding obfervations made at Greenwich and other places: 

 And that fome proper perfons be appointed to make the 

 obfervations, at the expence of the Society, that our lon- 

 gitude may be afcertained with the precifion that is necef- 



fary. It would be proper, that at leaft two fetts of obfer- 

 yers be appointed to view the tranfit in this city, in order 

 to guard againft the fatal accident oflofingthe Sun out 

 of the field of the telefcope, in the critical and important 

 moment; which I find happened to a good aftronomer ia 

 the Eaft-Indies, at the time of the laft tranfit. It is very 

 difficult to preferve a celeftial objea in the field of a telef- 

 cope, that magnifies confiderably. 



The expence of making thefe obfervations, withfufEcient 

 accuracy, muft be confiderable; but it is hoped that an op 



tiot be negleded on this account, which 



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portunity 



for its importance to the interefts of aftronomy and navi 

 gation, has juftly drawn the attention of ever 7 civilized na- 

 tion in the world, and which will not be prefented again 

 for more than a century to come. 



Thefe 



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