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.