( ) 
L The Longitude of Lisbon, and the Fort of 
New York , from Wanfled and London 
determined by Eclipfes of she Firfl Satellite Oj 
Jupiter. By the E^everend Mr. James Brad- 
ley, M. A. Aftron. Prof, Savil. R% S. S. 
S OME curious Agronomical Obfervations having 
lately been communicated to this Society from 
Lishorty among which were fcveral Eclipfes of the firft 
Satellite of Jupiter* ; I was willing to examine whether 
I had made any at Wanfled which tallied with them, that 
by comparing fuch together, the true Difference of 
Longitude between thofe Places might be found. 
But looking over my Obfervations of the firfl Satel- 
lite, made laft Year and the beginning of this, I meet 
only with Two Emerfions that were obferved the fame 
Night both at Lisbon and Wanfled. There are others, 
indeed, made within a few Days of each other, which 
may likewife be made ufe of to determine the Difier- 
^ ence of Longitude ; but not with the fame degree of 
Certainty, by reafon of the irregular Motion of the 
Satellite ; which I prefume, chiefly arifes from the 
Gravity of the other Satellites towards it. For altho’ 
the Efietfl of the Influence that the Satellites have on 
each other, is mofl: remarkable in the Second, whofe 
Motion will fometimesbe accelerated or retarded there- 
by, as much as amounts to 30 or 40 Minutes in 
time, in the fpace of about feven Months, or in half 
the Period in which the three innermofl Satellites re- 
ctum, to have nearly the fame Pofition with refpe^l to 
themfelves, and the Shadow of Jupiter ; yet the firll 
M fee ms 
Vidi Page <?o. 
V. 
