[ 549 ] 
comparing, therefore, the time of the emerfion of the 
firft fatellite obferved by this gentleman, with the time 
computed from thefe formula , the difference of lon- 
gitude between London, at St. Paul’s, and the place 
of obfervation at Lifbon, comes out to be 36' 6" ; and 
by feveral former correfponding obfervations the dif- 
ference had been found to be 3 6 10". By fome ob- 
fervations of the fame fatellite, fent me lately by the 
reverend P. Pezenas at Marfeilles, and which he had 
received from fome aftronomers at Lifbon, the dif- 
ference of longitude between London and Lifbon is 
fometimes 34/, and fometimes 35-': But it is to be re- 
marked of thefe gentlemen, that tho’ they both ob- 
ferved at the fame place, and thro’ refradting tele- 
fcopes of the fame length ; yet they fometimes differ 
from one another a whole minute, in the time of 
emerfion. 
M. Chevalier further mentions the obfervation of 
the eclipfe of the fun laft October, thro’ a telefcope of 
1 5 palms. He faw both the beginning and end, in a 
very clear air ; and fays, that the greateft quantity of 
the eclipfe was 1 1 digits and 5 minutes, which he 
meafured with a micrometer j but, unluckily, has not 
given us either the diameter of the fun, or that of the 
moon, which he might have meafured (for the eclipfe 
was annular), tho’ he was at the pains of meafuring 
all the digits, both in the increafe and decreafe of the 
eclipfe. He farther takes notice, that, at the time of 
the greateft obfcuration, the light of the fun was re- 
markably diminifhed ; and that they were able to fee 
Jupiter, Venus, and fome ftars of the firft and fecond 
magnitude 3 but he could not fee Mercury, on account 
4 
