1 6 I)?-. Herschei/s Observations on the 
pearances might either not happen at all, or fall upon different 
places in its orbit ; I answer, that a period of more than ten re- 
volutions, which I have included, is already a strong argument 
that no such change has taken place ; for if the satellite had 
but made a single rotation upon its axis more or less than it 
has made revolutions round Saturn, the change must amount 
to nearly one degree per revolution ; that is, to about ten de- 
grees during the time of my taking notice of it ; which is a 
quantity I think I might have perceived. However, to remove 
all doubt, we have some valuable observations of M. Bernard, 
who in the year 1787, also found the 5th satellite of Saturn 
subject to the same change of light that M. Cassini had ob- 
served. * Now, by joining those to mine, we have a short pe- 
riod of near 20 revolutions that agree together, so as to pre- 
clude all doubt of any intermediate change ; and therefore we 
cannot be liable to err, when we extend this period to all the 
397 revolutions since Cassini's lime, and by that means ascer- 
tain that the 3th satellite of Saturn turns upon its axis, once 
in 79 days, 7 hours, and 47 minutes. 
I cannot help reflecting, with some pleasure, on the disco- 
very of an analogy, which shews that a certain, uniform plan 
is carried on among the secondaries of our solar system ; and 
we may conjecture, that probably most of the moons of all the 
planets are governed by the same law; especially if it be 
founded on such a construction of the figure of the secondaries, 
as makes them more ponderous towards their primary planets. 
For, if even the 5th satellite of Saturn, which is at so great a 
distance from its planet, is affected by such a law T , of course the 
other satellites are not very likely to have escaped its influence. 
* See Me'moires de l’ Academe, 178 6 , page 378. 
