MADE AT LANCASTER, 61 



Longitude deduced from the lunar eclipse of Sept. 1 1th. 



If the ti«ie when the moon began to leave the earth's shadow"? h / "■ 

 be taken for the end of the eclipse, the longitude will be $5 6 44 



I West from 

 If the time of the moon's leaving the penumbrabe taken for > ^Greenwich, 



the end of the eclipse, the longitude will be 3 5 4 16 f 



Mean, 5 3 50 



By our maps, the borough of Lancaster appears to be about 

 4' 29" in time, west from the city of Philadelphia, which ad- 

 ded to 5 h 0'' 37", the longitude of the latter west from Green- 

 wich, will give 5 h 5' 6" for the difference of meridians be- 

 tween the borough of Lancaster and the observatory of Green- 

 wich; which differs but 24" in time from the mean of the six 

 lunar observations, and only 59" in time from the widest of 

 them. From this it is manifest, that very great dependance 

 may be placed in the lunar observations, for the determination 

 -of the longitude. 



In determining the longitude from lunar observations, we 

 have the advantage of increasing the number almost at plea- 

 sure, and rendering them so numerous, that the mean of all 

 the results shall be nearly as accurate as the lunar theory itself, 

 which seldom errs so much as 30" of a degree, and generally 

 much less. 



By looking over the longitudes as deduced from the eclipses 

 .of Jupiter's satellites, it will be seen that the results from De- 

 lambre's tables are much more uniform than those from the 

 .nautical almanac, particularly of the 1st, 3d, and 4th satellites; 

 with respect to the 2d, the nautical almanac appears to have 

 the advancage; but it is to be remembered, that the observa- 

 tions made at this place have been too few, and the period 

 •too short, to decide on a subject of such nicety: it is never- 

 theless probable, that when die period is extended, and the 

 number of observations increased on the eclipses of the 2d 

 satellite, that Delambre's tables will be found to be the most 

 accurate. 



If a mean of the longitudes deduced from the lunar obser- 

 vations, the eclipses of Jupiter's satellitesagrecably to Delam- 

 bre's tables, and tlie lunar eclipse be taken collectively, the 

 longitude of Lancaster will appear to be 5 h 5' 0".6; and if 



