No previous inspection of pictures of these rings
can rob them of their effect upon the eye and the mind. They are
overwhelming in their inimitable singularity, and they leave every
spectator truly amazed. Sir John Herschel has remarked that they have
the appearance of an "elaborately artificial mechanism." They have even
been regarded as habitable bodies! What we are to think of that
proposition we shall see when we come to consider their composition and
probable origin. In the meantime let us recall the main facts of
Saturn's dimensions and situation in the solar system.

Saturn is the second of the major, or Jovian, group of planets, and is
situated at a mean distance from the sun of 886,000,000 miles. We need
not consider the eccentricity of its orbit, which, although relatively
not very great, produces a variation of 50,000,000 miles in its distance
from the sun, because, at its immense mean distance, this change would
not be of much importance with regard to the planet's habitability or
non-habitability. Under the most favorable conditions Saturn can never
be nearer than 744,000,000 miles to the earth, or eight times the sun's
distance from us. It receives from the sun about one ninetieth of the
light and heat that we get.

[Illustration: SATURN IN ITS THREE PRINCIPAL PHASES AS SEEN FROM THE
EARTH. From a drawing by Bond.]

Saturn takes twenty-nine and a half years to complete a journey about
the sun. Like Jupiter, it rotates very rapidly on its axis, the period
being ten hours and fourteen minutes. Its axis of rotation is inclined
not far from the same angle as that of the earth's axis (26 deg.
49 min.), so that its seasons should resemble ours, although their
alternations are extremely slow in consequence of the enormous length
of Saturn's year.

Not including the rings in the calculation, Saturn exceeds the earth in
size 760 times. The addition of the rings would not, however, greatly
alter the result of the comparison, because, although the total surface
of the rings, counting both faces, exceeds the earth's surface about 160
times, their volume, owing to their surprising thinness, is only about
six times the volume of the earth, and their mass, in consequence of
their slight density, is very much less than the earth's, perhaps,
indeed, inappreciable in comparison.

Saturn's mean diameter is 73,000 miles, and its polar compression is
even greater than that of Jupiter, a difference of 7,000 miles--almost