[ 482 ] 
lev’s tables has followed that determination, which 
has alfo been generally ufed by the Englith Aftrono- 
mers . — The French Aftronomers have till very lately 
imagined the difference of meridians to be 9'. i° • 
as deduced from a fingle obfervation of an eclipie o 
Jupiter’ s firft fatellite made by Mr. Caffini when m 
London, with a telefcope of fimilar fize and con- 
ftru&ion with that ufed at Paris when the lame eclipie 
was obferved. — In the year 1734 Mr. Maraldi pub- 
lilhed a comparifon of 33 eclipfes obferved at Green- 
wich by Mr. Flamfteed, and at Paris by the French 
Aftronomers, 19 of which are immerfions, and the 
reft emerfions. The longitudes refulting from each 
correlpondent obfervation differ widely from each 
other, the two obfervatories being n'. 2 j" diftantby 
an immerfton of the 2d fatellite, and only 7 43 b Y 
an emerfion of the firft. But if we take a mean of 
the whole, the difference of longitude will be 9 .24 ; 
and if we exclude the obfervation of the 2d fatellite 
above mentioned, which muft be very faulty, the dif- 
ference of meridians will be g'. 22", arefult which in 
all probability is but a very few feconds from the truth. 
• It may be obferved that the immerfions all give the 
difference of longitude too great, and almoft all the 
emerfions too little j a circumftance owing either to 
the badnefs of the air here in England, or to an in- 
equality in the goodnefs of the telefcopes, or per- 
haps to both ; for whatever was the advantage in ob- 
ferving the immerfions, was ballanced by the emer- 
iions : for which reafon whenever the eclipfes ot Ju- 
piter’s fateliites are ufed, the longitude Ihouid, it potii- 
ble be deduced both from immerfions and emerfions. 
As the obfervations of tranfits of Mercury may be 
very ufeful in fettling the longitudes of places which 
