*7 
Rotation of the fifth Satellite of Saturn. 
From the considerable change in the brightness of the 5th 
satellite of Saturn, we may be certain that some part of its sur- 
face, and this by far the largest, reflects much less light than 
the rest ; and, from the points of its orbit in which it appears 
brightest to us, we conclude that neither the darkest nor 
brightest side of the satellite is turned towards the planet, but 
partly one and partly the other ; though probably rather less of 
the bright side. 
The great regularity of this change of brightness seems to 
point out another resemblance of this satellite with our moon. 
It is well known that we see the spots of the moon pretty 
nearly of the same brightness, so as not to be overcast in a 
very strong degree by dense clouds to disfigure them, and 
therefore have great reason to surmise that her atmosphere 
is extremely rare ; which indeed we also know from other 
principles : In like manner, on account of the uninterrupted 
changes in the brightness of the 5th satellite of Saturn, we 
may suppose that it also partakes of a similar fate with respect 
to its atmosphere, which is probably as rare as that of our 
moon. 
On the Distance of the fifth Satellite. 
The distance of the 5th satellite from Saturn is allowed to 
be the most proper for obtaining a true measure of the quan- 
tity of matter contained in the planet ; for which reason I have 
taken many measures of it with the 20-feet reflector. I give 
them at full length, that the validity of them may appear in 
its proper light. 
Sept. 25, 1791. Correction of the clock — 2' 19", 5 for midnight. 
Distance of the 5th satellite of Saturn from the centre of the 
MDCCXCII. D 
