distance of the real Sun. This idea does not, however, now find favour.

Of the four chief satellites, the two inner ones are in size much the same as our Moon, and the two outer ones are both larger than Mercury. They, like our Moon, are in reality planets travelling round and with Jupiter, and with him round the Sun. The views of Jupiter, seen from any of them, must often be magnificent, more especially from the nearer ones.

IV. A WONDROUS PLANET

Saturn, like Jupiter, is head of a small system of his own, within the Solar System. But his is a more marvellous family than that of Jupiter.

In size this planet is rather the smaller of the two, and a good deal lighter in make, lighter in fact than water. If the whole big body of Saturn could be plunged into some vast ocean of water—and that ocean would have to be vast indeed for such a purpose!— the globe would float as if it were an india-rubber ball. This is a fact, known, not guessed. Strange though the idea may seem, heavenly bodies can be actually weighed from Earth, as if they were put into huge scales, one against another. And the mode in which it is done is by observing and calculating the pull of one body on another. In this manner the actual avoirdupois weight of the Moon, of planets, of the Sun, and even of certain stars, has been reckoned.

Saturn, too, has greatly flattened poles and a very bulging equator, and his big body spins rapidly round in little over ten hours. Apparently he is covered with

immense masses of clouds, though the signs of furious disturbances, ever present on Jupiter, are not so evident here. But we have to allow for the enormously increased distance, making it so much more difficult for us to see what goes on.

This large planet has been described as "a world in the making," which phrase might equally well be used for Jupiter, and, no doubt, for Uranus and Neptune.

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The making in Saturn's case seems not to have advanced so far as even with Jupiter. Though smaller than his gigantic twin, he shows signs of being even less cooled, which is curious.

Not only has Saturn a family of ten moons-very likely more than ten-but also he is surrounded by an extraordinary set of Rings, unlike anything possessed by any other member of the Sun's family.

Of the moons, the largest, Titan, is about the same

size as Mercury, and takes rather more than a fortnight to journey round its big planet. But Mimas, the nearest, has to rush round in twenty-two hours, so strong is the drawing which otherwise would drag it down into that heated, cloudy surface. And while Saturn's day is only a little over ten earthly hours, his "year lasts through nearly thirty of our years, as already stated.

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And the Rings, those wonderful Rings which mark Saturn out as apart from all other worlds!

It is commonly said that they are three in number, one over another; that is, they are placed farther and farther away from the body of the planet. They are very wide, stretching outward from the globe, passing round the whole of it, over its equator.

To see clearly what this means, get a small globe or a large apple, and a piece of ribbon long enough to go easily once round it. Now fold the ribbon round the apple like a sash, lying flat on it. But that will not do as a picture of the Rings. You have to hold the ribbon against the apple, not lying flat, not with its width against the skin, but with its edge only touching. One edge of the ribbon must rest on the apple, and the other edge must stand outwards away from it. That is how the Rings are placed.

They are extraordinarily wide, outward from the planet, and extraordinarily narrow, as seen from the surface of the planet, underneath them.

Here are the measurements, given roughly.

To begin with, Saturn's own diameter is more than seventy-six thousand miles.

If a man stood on the equator-supposing, again, that any human being could stand there-all he would see of the Rings just overhead, if he could see anything of thern at all, would be a thin line or edge, crossing the sky five or six thousand miles distant. For the Rings, like the piece of ribbon on the apple, would not lie flat over his head, but would be placed edgeways, stretching up and away, and presenting to his gaze only a narrow line.

If he wished to see more, he would have to travel away from the equator, south or north, to a position where he might gain a sideways view of the Rings; not merely of the lowest, but of the great width of all three, extending upward. Then, indeed, if other circumstances, such as the sunlight falling in the right direction on them, were favourable, he would seesomething!

Beginning at less than six thousand miles from the planet-or from its cloudy envelope-lies the Crape Ring, so called from its transparent nature. It reaches upward for nearly eleven thousand miles.

Then comes a gap, and after it another Ring; the Inner Ring, a very bright one, reaching up and up for another eighteen thousand miles.

Then a second gap, over two thousand miles wide, followed by a third Ring, the Outer One, eleven thousand miles wide; still always reckoning the width as upward and away from the planet.

We on Earth have in telescopes a clear view of these Rings, lying one outside another, when we happen to be in a right position. But at times, when we happen to be—not, like the supposed man, just under them,

UNIV. OF

but actually just over them-then we, too, see them simply as a faint line, hardly visible.

What are these Rings? What are they made of? They were once believed to be actual rigid Rings, solid and fixed, revolving as a whole round the planet. But this was proved to be impossible. The tremendous pull of that great world, acting on a structure part of which lay so near and part so far away, must long ago have broken it up.

What now is believed, and is accepted as practically certain, is that they are formed of countless multitudes —millions of millions of millions of tiny bodies, which whirl incessantly at tremendous rates of speed round Saturn, each in its own separate orbit. Practically, each one is a minute satellite, living its own small life like any other satellite.

But imagine what must be the enormous numbers of them, to make the Rings visible to us at this immense distance. Think, too, how great the speed, if it can prevent them from falling down on the body of the planet.

No doubt the partial transparency of the inner Crape Ring is brought about by the small bodies not being so plentiful-not so crowded together as in the outer Rings.

This theory about their make has gained remarkable support through the spectroscope. Not only was it found that the different Rings did not travel all together at the same pace, as they must have done were they one solid structure; but also the parts of each Ring nearer to Saturn went faster than those more distant,