Page:Popular Science Monthly Volume 51.djvu/374

362 less as the distance from the main ring increases, until the eye can no longer detect their mass and the ring apparently ends.

This explains why the outline of the planet can be seen through the dark ring; but if this fact is not enough, an observation made on November 1, 1889, at the Lick Observatory will further confirm the theory. This observation was of the outer satellite, which was in such a position behind the planet as to pass through the shadow of the rings and be eclipsed by it. Watching the satellite, then, as it left the planet's shadow and slowly passed on into the shadow of the rings, its light was seen to grow gradually fainter as it passed through the shadow of the dark ring, but did not wholly disappear until the moon had entered the shadow of the inner bright ring. This shows clearly that the dark ring is partially transparent, but becomes more opaque as the bright ring is approached.

With regard to the satellites there is little to be said. There are eight known at present, and there may be more, for they are mostly quite small, as heavenly bodies go. Still, they form the most numerous as well as the most extended family within the sun's domain, for the outer one of all swings around Saturn at a distance of two and a quarter millions of miles—ten times as far away as our own moon. This one, which is named Japetus, is just about the size of the moon, and apparently shares the latter's peculiar trait of always keeping one side toward its ruling planet. This supposition is due to the fact that when on the western side of Saturn Japetus is always very much brighter than when to the eastward; in fact, though easily seen with a telescope of moderate power when brightest, it will almost entirely disappear when faintest. It is difficult to explain the cause of such a marked change, for one half of the satellite must be extremely bright and the other half very much darker to produce it, but the fact remains.

Titan, as its name implies, is the largest of the group, and in size is midway between Mars and Mercury—in fact, it would make a very respectable planet itself, for it is nearly half the diameter of the earth. The other six are all considerably smaller than our moon, and have been discovered in the order of their brightness, their discovery keeping pace with the increase in the power of telescopes, so it is quite possible that there may be others in this already numerous family to be introduced later on.

We spoke in the beginning of this article of destroying the theories often put forth concerning the inhabitants and conditions of life upon this far-off world. There are certain facts and deductions, however, from which we can gain an idea of some of the conditions which may prevail when Saturn has finally reached a stage where life will be possible upon its