[ > 8 7 ] 
ing of this theory might perhaps depend upon the 
quantity of this inequality, which Mr. de Fouchy 
has not determined, not having been at leifure, to 
refume the fubjecft, flnce the ye nr 1732. The feg- 
ment of the difc, which is not eclipled, when the 
fatellite difappears, mu ft vary in the proportion of 
the fquares of the diftances of Jupiter from the Sun, 
and from the Earth. This is what a little reflec- 
tion will make evident to every one, and this is the 
firft caufe of the inequality. Since Mr. de Fouchy’s 
obfervation, it has been difcovered, that the light of 
the fatellite likewife decreafes, in proportion to the 
proximity of Jupiter’s difc ; the brightnefs of the 
planet weakens that of the fatellite, and, for this 
reafon, the eclipfes, which happen too near the op- 
pofition [of Jupiter to the Sun], are looked upon 
as defective. Befides, the light of Jupiter, as 
well as that of his fatellites, is different, in his 
different 
non^ais, que la perfection de cette theorie dependrait peut etre 
de la quantite de cette inegalite, que Mr. de Fouchy n’a point 
ddterminee ; il n’a pu s’en occuper depuis 1732. II refulte de la 
confideration du fegment du difque, qui n’eft pas eclipfe, quand le 
fatellite difparait, que ce fegment varie en raifon \inverje\ des 
quarres de la diftance de Jupiter au Soleil, et de la diftance de 
Jupiter a la Terre. Voila la premiere caufe d’inegalite. Depuis 
Mr. de Fouchy, on s’eft apper^u que la lumiere du fatellite di- 
minuoit encore en raifon de la proximite du difque de Jupiter j 
l’eclat de la planete efface celui du fatellite, c’eft pour cette raifon 
que les eclipfes, qui arrivent trop pres de l’oppofition, font regar- 
dees comme defe&ueufes. De plus, la hauteur de Jupiter fur 
Thorifon contribue aufii a affoiblir fa lumiere, et celle de fes fa- 
Vol. LXIII, C c tellites 5 
