for us to live on her outer surface, is by no means thoroughly cool all through, but is believed to be exceedingly hot still, deep down inside.

All this complicates still more the difficult question of life or non-life on Mars.

It may be that the living history of Mars lies in the far past, that it is over now, and that the little planet, like some used-up hulk, tossed aside, floats on the wide expanse of Space, no longer the abode of living beings.

Yet, even if it were so—and we have no proof whatever that it is-who should venture to say that no further use for Mars can exist in the ages to come? The very materials of some old used-up hulk may be re-fashioned into new shapes for use and for beauty. There are not only mysteries, but also possibilities, in the story of the Universe, beyond our ken.

PART VII

GIANT WORLDS

I.—LITTLE AND GREAT

BETWEEN Mars and the next important member of the Sun's family lies a wide space, occupied by a number of very small bodies, commonly now spoken of as THE MINOR PLANETS. In the past they were known as the "Asteroids" or Little Stars; then as the "Planetoids " or Little Planets; which last they are, but not stars.

The biggest of these, Ceres, is only about four hundred and eighty miles in diameter, a mere pigmy beside our Moon; and thence they range downward to what are simply large balls rolling through the sky. At first their numbers were supposed to be few, perhaps twenty or thirty at most. But more and more were gradually sighted and named and charted, till now at least close upon a thousand are known to astronomers. How many hundreds or thousands more may remain to be discovered time alone can show.

For a good while they were believed to keep strictly to a certain limited district or belt, in the regions which divide the orbit of Mars from the orbit of Jupiter, behaving in a most orderly and obedient fashion; obedient, I mean, to our ideas of what they might be expected to do.

But in recent years some wandering members of that company have been found outside the said limits.

One of these, Eros by name, is especially interesting. Not on account of its size; for it is a mere ball, perhaps only twenty miles through, or about the size of Mars' moon, Phobos; but on account of its position. Instead of keeping to the wide belt which is followed by most of its companions, this ambitious planetoid during part of its year-for even minor planets have their own separate years "--travels right away between Mars and Earth. It actually has the selfassertion to draw much closer to us than any other heavenly body in the sky, except our Moon; nearer than our next-door neighbours, Mars and Venus.

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Another minute minor, no less adventurous, and so unimportant in itself that it can boast no name, but is distinguished simply as T. G. 588, instead of coming farther this way, goes farther off than any one would expect. During part of its " " it has the presumption to approach very nearly, if it does not actually cross, Jupiter's pathway.

year

The contrast between this tiny ball and the vast bulk of Jupiter makes one irresistibly think of Landseer's famous picture, “Dignity and Impudence.

It was long held that the minor planets might be scattered remnants of a single large world, which had somehow broken up or gone to pieces in ages past, scattering its pieces far and wide. This is not now generally looked upon as so likely. They are regarded rather as genuine small planets, each having its own individual pathway round the Sun, though each is

perpetually swayed and influenced by the drawing power of bigger heavenly bodies passing near.

Leaving Mars behind us, with only this brief glance

by the way at the hundreds of little hurrying bodies between, we journey on to the giant-world of our System, JUPITER. And that giant-world lies nearly five times as far off from the central Sun as our Earth

does. Think of that !—five times ninety-three millions of miles! Not easy to picture in one's mind.

Other worlds lie farther still. Jupiter's twin-giant, SATURN, has the next nearest position. But Saturn's orbit is about twice as far from the Sun as Jupiter's orbit, which it encircles. The third great outer planet, URANUS, follows his lonely path, twice as far from the Sun as that of Jupiter; and the fourth, NEPTUNE, lags along his dim and dreary way, as far from Uranus as Uranus is from Saturn.

Huge planets all of these, though the two last-named are not nearly so huge as the two first. All four shine, like the lesser worlds, with the borrowed radiance of sunlight; though it is thought probable that they also give forth some shining of their own.

But not one among them all is so brilliant an orb, seen from Earth, as Jupiter. Venus alone in our sky can outshine him.

Like Venus and Mars, he does not beam upon us at all times with equal brightness; for sometimes he is more near, being on the same side of the Sun as we are; sometimes he is more distant, being on the opposite side. And even when he and we are on one side, the dividing distance varies much, because of the extremely oval—or elliptic shape of Jupiter's pathway. It is only about once in twelve years that the two planets reach their very nearest points, so that we see our big brother-world at his very best. Then he is indeed beautiful.

Jupiter is by far the biggest world in our System, though Saturn comes near enough to be called his "twin." Our Earth and her twin, Venus, are each