78 Dr. Herschei/s Discovery of four additional 
within its reach ; for they have very little light to lose, and lose 
it pretty suddenly. 
This contrast, therefore, between the condition of the Georgian 
satellites and those of the brighter planets, seems to he suffi- 
cient to account for the phenomenon of their becoming invi- 
sible. 
We may avail ourselves of the observations that relate to the 
distances at which the satellites vanish, to determine their re- 
lative brightness. The 2d satellite appears generally brighter 
than the 1st; but, as the former is usually lost farther from the 
planet than the latter, we may admit the 1st satellite to be 
rather brighter than the 2d. This seems to he confirmed by 
the observation of March 9, 1791 ; where the 2d appeared to be 
smaller than the 1st, though the latter was only 25" from the 
planet, while the other was 30", 8. 
The first of the new satellites will hardly ever be seen other- 
wise than about its greatest elongations, but cannot be much 
inferior in brightness to the other two ; and, if any more in- 
terior satellites should exist, we shall probably not obtain a sight 
of them; for the same reason that the inhabitants of the Georgian 
planet perhaps never can discover the existence of our earth, 
Venus, and Mercury. 
The 2d new or intermediate satellite is considerably smaller 
than the 1st and 2d old satellites. The two exterior, or 5th and 
6th satellites, are the smallest of all, and must chiefly be looked 
for in their greatest elongations. 
Periodical Revolutions of the new Satellites. 
It may be some satisfaction to know what time the four 
