hB 



MATHEMATICAL and 



-with the Sun November 9th, i 769. The internal contact 

 n-ixxt It fornething more; owing no doubt to the difference 

 that will arife among obfervers, in determining the exad 

 moment when the thread of light is compleated; and the 

 mean of all our other obfervations, gives the_ difference of 

 meridians, between A^orr/V^K and Philadelphia, only 4" of 

 time more than the terrelirial meafurcment, and tlie exter- 

 nal contad oi Mercury gave it, which may be taken as a 

 very rreat degree of exaftnefs for celeftial obfervations; if 

 we confidcr that the difference of meridians, between the 



For he fays " 

 but that he him- 



long eftablilhed obfervatories of Grecnivich and 1 arts, as 



Mr. De La Lande writes, November iSth, 1762^, was 

 not then determined within 20" of time 

 fome called it 9''. 15"; others 9'. 40"; 

 felf commonly ufed 9' . 20", though he could not telJ from 

 what obfervations it was deduced." And it may be need- 

 lefs to add that a fhort diffance is as liable to the differences 

 arifm"- from the ufe of inftruments in celeftial obfervations, 

 as a greater one. Neverthelefs, if we apply the difference of 

 meridians between Philadelphia and Norriton, got by this 

 meafurement (viz. 52", inftead of 56",) to the Revd. Mr. 

 Eimn'r\ colleaion of Jupiter's fatellites, (p. 55), rejeamg 

 thofe of the 2d fat. and alfo the immerfions of May 5th, as 

 too near the oppofition, we Ihall get Philadelphia, $"■ o[. 

 -77", andNorrlton, 5^- i' .29",weilfrom GreenAich. This 



refult is what ought to arife from a diminution of 4" of 

 time in the difference of meridians, by dividing that dif- 

 ference, and bringing the one meridian 2" more wefl, and 

 the other 2" moreeaff; and we believe future obfervations 



will confirm this as exceeding near the truth. 



The latitude of Norriton comes out, by the meafurcment, 



,ty 



ttenhoufi 



tlons o^ive it; and if the latitude of that point of the city be 



conds) 



MefTrs. Maji 

 oi Norriton 



40^.9' 3 



40". 9^ 56 



ever. 



f I 



