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of its rush, we see what looks like a star flashing along in the sky and vanishing. But it is not a star. It is only a captured meteorite.

In less than a second, during which it may have travelled twenty miles or more, the small body has ceased to shine, because it has ceased to be. A tiny shower of dust drops quietly down, and that is the end of the "shooting star.

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Once in a while, if the meteorite should be unusually large, part of it reaches the ground as a solid and very hot lump. But this comes to pass so seldom, in comparison with the numbers which simply disappear, that we can only suppose the big specimens to be very few as compared with the small ones. At all events, it seems to be so in those parts of the sky where our Earth journeys.

Such a solid body arriving here is called an Aerolite, and aerolites have been often found to be largely made of iron. Some of them may once have formed part of a comet's head.

At certain seasons of the year we touch on streams of meteorites, and see many more shooting stars than in other months; and now and again, at long intervals, our Earth has passed through a vast horde of these little bodies, plunging into the midst of them as a swimmer might plunge into a shoal of fish. A grand sight has then been witnessed. Thousands and thousands of bright meteors were watched, hour after hour, flashing and dying in the heavens.

Meteorites are believed to congregate in countless myriads of legions, around and about in the neighbour

hood of the Sun; and the Zodiacal light, seen at times from Earth, is supposed to consist entirely of them.

So too, as we found earlier, do the Rings of Saturnmillions of millions of little bodies ever whirling round that great world, and journeying with him round the Sun.

Moreover, it has been thought that the Earth and all her brother and sister-worlds were once upon a time masses of loose meteorites, held together by their mutual attraction, and gradually, slowly, through ages, drawing closer and closer together, as they passed from stage to stage on the road to becoming solid. This was mentioned a little earlier, and we have had glimpses of those successive stages in the history of Saturn, of Jupiter, of Mars, of Earth, of the Moon.

But one great example of an intermediate stage, between the loose condition of separate meteorites and the seemingly liquid condition of Saturn, has not yet been brought forward. That is the Sun-stage.

It may well be that the raw material, out of which has been fashioned this Solar System-Sun, Moon, Earth, planets, satellites, comets—at a certain stage of development consisted simply of meteorites. But this does not bring us anywhere near the beginning of things. Tracing back from small solid meteorites, we come to fine meteoric dust, of which comets' tails may be largely composed, and vast quantities of which probably exist throughout our whole System. And that fine dust, traced still farther back, would no doubt land us amid enormous masses of slowly revolving beyond the gases-who can say what next?

gases. And gases.

But all such theories should be taken cautiously and held lightly. In speaking of the far-past we do not know, we can only conjecture. In the end they may prove to have been right theories, or they may have to give place to other explanations.

PART IX

DISTANCES AND MEASUREMENTS

I. A REDUCED SCALE

To bring before our minds a clearer notion of what is really meant by the distances of our Solar System, we will try now to picture the whole on a smaller scale, less difficult to grasp than the real figures.

You still have to think of the whole family belonging to our Sun as one great system; but as lessened everywhere throughout in size, while keeping just the same proportions, each with respect to the rest.

So we will let ONE INCH stand for ONE THOUSAND MILES, both for sizes and for distances. Thus, two inches will mean two thousand miles, three inches will mean three thousand miles, and so on.

All the planet-distances given here are from the Sun, not from the Earth. We take the Sun as the centre, which he is, and reckon outwards from him, counting our Earth for what she actually is-one small world among many, and not in size even one of the most prominent.

First we must have the Sun, a radiant, blazing body about seventy feet in diameter. Picture a large ball, dazzlingly bright, as high and as wide every way as a good-sized house. And each inch in its height

and breadth and entire make stands for one thousand miles.

Mercury, a small ball three inches in diameter, travels round the Sun at a distance of five-ninths of a mile. Venus, nearly eight inches in diameter, travels round one mile away.

Earth, matching Venus in size with her Moon about twenty feet off-travels round at a distance of one mile and a half.

Mars, only four inches in diameter; two miles and one-fifth away.

Then a considerable company of very minute Minor Planets, scattered round in a belt, to which most of them keep.

Jupiter comes next-a big globe, seven feet in diameter; journeying round at a distance of seven miles and a half from the Sun.

Saturn, six feet in diameter; on an orbit fourteen miles from the Sun.

Uranus, thirty-two inches in diameter; twenty-eight miles distant.

And Neptune, thirty-five inches in diameter; fortythree miles away from the Sun. For all his seventy feet of diameter, that Sun by this time will have sunk to a very small object.

The whole Solar System, thus reduced, one inch standing everywhere for a thousand miles, would be contained within a circle of about one hundred miles in any direction. Some of the comets alone would travel outside this limit. The diameter of each planet-orbit, that is, its breadth across from one side to the other, is twice the distance of that planet from the Sun. So Neptune's

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