rk the
place of the planet with regard to the stars in its vicinity. Those who
are privileged to use accurate astronomical instruments can readily
detect the motion of Saturn in a few hours.

The average distance from the sun to Saturn is about 886 millions of
miles. The path of Saturn, as of every other planet, is really an
ellipse with the sun in one focus. In the case of Saturn the shape of
this ellipse is very appreciably different from a purely circular path.
Around this path Saturn moves with an average velocity of 5.96 miles per
second.

The mean diameter of the globe of Saturn is about 71,000 miles. Its
equatorial diameter is about 75,000 miles, and its polar diameter 67,000
miles--the ratio of these numbers being approximately that of 10 to 9.
It is thus obvious that Saturn departs from the truly spherical shape to
a very marked extent. The protuberance at its equator must, no doubt, be
attributed to the high velocity with which the planet is rotating. The
velocity of rotation of Saturn is more than double as fast as that of
the earth, though it is not quite so fast as that of Jupiter. Saturn
makes one complete rotation in about 10 hrs. 14 min. Mr. Stanley
Williams has, however, observed with great care a number of spots which
he has discovered, and he finds that some of these spots in about 27 deg.
north latitude indicate rotation in a period of 10 hrs. 14 mins. to 15
min., while equatorial spots require no more than 10 hrs. 12 min. to 13
min. There is, however, the peculiarity that spots in the same latitude,
but at different parts of the planet, rotate at rates which differ by a
minute or more, while the period found by various groups of spots seems
to change from year to year.

These facts prove that Saturn and the spots do not form a rigid system.
The lightness of this planet is such as to be wholly incompatible with
the supposition that its globe is constituted of solid materials at all
comparable with those of which the crust of our earth is composed. The
satellites, which surround Saturn and form a system only less
interesting than the renowned rings themselves, enable us to weigh the
planet in comparison with the sun, and hence to deduce its actual mass
relatively to the earth. The result is not a little remarkable. It
appears that the density of the earth is eight times as great as that of
Saturn. In fact, the density of the latter is less than that of water
itself, so that a mighty globe of water,