C ! 59 ] 
found by M. Caflini, by obfervations of the eclipfes 
of Jupiter’s firft fatellite made by him, whilft in Lon- 
don in the year 1698 : we are no where told, that 
I know of, by what obfervations the Englifh aftro- 
nomers have fixed this difference at g' 20 " . 
In the Memoirs of the Royal Academy of Sciences 
at Paris, for the year 1734, there is an account given 
of thirty-three correfponding obfervations of the 
eclipfes of the firft fatellite of Jupiter, made at 
Greenwich and Paris, from the year 1 677, to the 
year 1701 : The mean of thefe thirty-three obfer- 
vations gives the difference of longitude between Pa- 
ris and Greenwich = g' 2g" . 
I had lately the honor to deliver to this Society, a 
paper concerning the parallax of the Sun, determin- 
ed by the obfervations of the late tranfit of Venus : 
Jn that paper I took notice that obfervations of the 
tranfits of Venus and Mercury over the Sun, have al- 
ways been looked upon by aftronomers, as very pro- 
per for determining the differences of longitudes be- 
tween the places where fuch obfervations have been 
made. I have calculated, and it may be demonftrat- 
ed, that, if we compare the obfervations of the late 
tranfit of Venus made at Greenwich, and by M. de^ 
la Lande at Paris, and fuppofe that the difference of 
longitude between thefe two places is — g' 25' , it 
will follow that the Sun and Venus are at an infinite 
diftance, which is abfurd. Again, if we fuppofe the 
difference to be greater, it will follow, that the Sun 
and Venus are more than infinitely diftant, which is 
likewife abfurd. We are therefore certain, if thefe 
obfervations are to be depended on, that the differ- 
ence of longitude between Greenwich and Paris is 
lefs 
