348 Dr. Herschel's Observations of the 
brightness were wanting ; and sometimes also to the magni- 
tude of the 4th, and even of the 3d. 
The 3d satellite can hardly be ever compared to any but 
the 2d in magnitude; and this only in its degree of excess. 
The magnitude of the 4th satellite has been generally com- 
pared with that of the 1st; and also sometimes with that of 
the 2d. 
To make an application of the contents of the figures, will 
now require little more than a bare inspection of them. 
The 1st satellite appears evidently to have a rotation upon 
its axis that agrees with its revolution in its orbit. It cannot 
be supposed that, in the course of 470 revolutions, all the bright 
observations could have ranged themselves in one half of the 
orbit, while the faint ones were withdrawn to the other. The 
satellite appears in the middle of the duration of its brightness, 
when it is nearly half way between its greatest eastern elon- 
gation, in the nearest part of its orbit ; or when advancing to- 
wards its conjunction. I have pointed out this circumstance 
by a division with dotted lines, and the words bright and faint, 
inserted within the circle, fig. 1 . This satellite, therefore, re- 
volves on its axis in i d i8 h 2 6', 6. 
The 2d satellite, though much less subject to change, on 
account, as we may suppose, of having only a small region on 
its body which reflects less light than the rest; has, never- 
theless, its rotation directed by the same law with the 1st. It 
will hardly be necessary to take notice of a single deviation 
which occurs at 163 degrees, fig. 2. ; as from the proximity of 
the satellite to the conjunction, a mistake in the estimation may 
easily take place. I generally made it a rule not to make 
