This brings us again to the consideration of those marvelous appendages, and to the statement of facts about them which we have not yet recalled.

If the reader will take a ball three inches in diameter to represent the globe of Saturn, and, out of the center of a circular piece of writing-paper seven inches in diameter, will cut a round hole three and three quarter inches across, and will then place the ball in the middle of the hole in the paper, he will have a very fair representation of the relative proportions of Saturn and its rings.  To represent the main gap or division in the rings he might draw, a little more than three eighths of an inch from the outer edge of the paper disk, a pencil line about a sixteenth of an inch broad.

Perhaps the most striking fact that becomes conspicuous in making such a model of the Saturnian system is the exceeding thinness of the rings as compared with their enormous extent.  They are about 170,000 miles across from outer edge to outer edge, and about 38,000 miles broad from outer edge to inner edge—­including the gauze ring presently to be mentioned—­yet their thickness probably does not surpass one hundred miles!  In fact, the sheet of paper in our imaginary model is several times too thick to represent the true relative thickness of Saturn’s rings.

Several narrow gaps in the rings have been detected from time to time, but there is only one such gap that is always clearly to be seen, the one already mentioned, situated about 10,000 miles from the outer edge and about 1,600 miles in width.  Inside of this gap the broadest and brightest ring appears, having a width of about 16,500 miles.  For some reason this great ring is most brilliant near the gap, and its brightness gradually falls off toward its inner side.  At a distance of something less than 20,000 miles from the planet—­or perhaps it would be more correct to say above the planet, for the rings hang directly over Saturn’s equator—­the broad, bright ring merges into a mysterious gauzelike object, also in the form of a ring, which extends to within 9,000 or 10,000 miles of the planet’s surface, and therefore itself has a width of say 10,000 miles.

In consequence of the thinness of the rings they completely disappear from the range of vision of small telescopes when, as occurs once in every fifteen years, they are seen exactly edgewise from the earth.  In a telescope powerful enough to reveal them when in that situation they resemble a thin, glowing needle run through the ball of the planet.  The rings will be in this position in 1907, and again in 1922.

The opacity of the rings is proved by the shadow which they cast upon the ball of the planet.  This is particularly manifest at the time when they are edgewise to the earth, for the sun being situated slightly above or below the plane of the rings then throws their shadow across Saturn close to its equator.  When they are canted at a considerable angle to our line of sight their shadow is seen on the planet, bordering their outer edge where they cross the ball.