his great kindness in helping me with the corrections of my book, Sun, Moon and Stars. We were speaking about the planets and their possibilities. He said thoughtfully-what led to it I do not recall

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Who knows? They may all be just chips struck from the block in the making of our Earth!"

Who knows indeed? A sculptor will ruthlessly strike away masses of marble, to set free the vision of beauty which he but no other man-already sees enshrined in a shapeless block.

II. STAR-CLUSTERS AND NEBULÆ

Among the many wonders of our Starry Universe, not least are the Star-clusters and Nebulæ. Large numbers of both are known to astronomers, and a certain number can be seen by the naked eye as faint cloudlets or dim and misty smudges in a clear sky.

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The word " nebula " is Latin for "cloud; " and when the expression "nebulous " is used it means "cloudy or "hazy."

It is not an easy matter to draw an exact line between clusters and nebulæ. Some star-clusters can be separated by a telescope entirely into stars. Some nebulæ cannot be separated at all into distinct stars. But many

clusters are made up partly of stars and partly of gasmasses; and many nebulæ also are the same—partly stars, surrounded by vast masses of gas or "nebulosity."

One well-known star-cluster in the constellation Centaur, just visible to the unaided eye, has thousands of stars packed together in a space of sky just twice the diameter of our Moon as she appears to us. Another

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cluster is that of the Pleiades, where, though we commonly see only six or seven stars, hundreds are really crowded among the six or seven. This does not mean that the hundreds in either case are actually "packed" or crowded," but only that they seem so through distance. Each star in those clusters may be very far from all its neighbours.

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Many years ago it was confidently believed that both clusters and nebulæ were made up entirely of stars, pressed together and rendered dim simply by the fact that they were so very far away. It was maintained that only a powerful enough telescope was needed to resolve them one and all into groups of distinct star-points.

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But though some thus yielded to increased telescope powers, others declined to do anything of the kind. And with the advent of the spectroscope, fresh tidings arrived from dim and distant regions.

For certain of these nebulæ, which had obstinately refused to be separated by the telescope, were examined by means of the spectroscope; and they made a most unexpected response. In plain terms they were requested to write their signatures, as countless other stars had done. And they did not refuse; but the style of signature came as a surprise. No soft bands of colour appeared, as with our Sun and with stars in general. Only bright lines were seen. And this said plainly that the nebula itself must be made, chiefly if not wholly, of gaseous matter.

Among some of the best-known nebulæ is a very fine one in Orion, easily seen by the naked eye. Small

and dim as that hazy smudge seems to us, it is enormously large and enormously distant. Another grand one is in Andromeda; not grand as seen without help, but very much so through a powerful telescope, or when photographed. Looking at a clear and good presentation of this marvel, one cannot but realise, from the curious whirlpool or maelstrom appearance, that the vast gas-masses must surely be whirling steadily around a centre. It may well be so; not with this particular nebula only. Stars are whirling; why not nebulæ also, from which we believe stars and systems of stars to spring?

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We have seen the Sun in his splendid youth; so much less developed than the planets or our Earth. Starclusters must be younger still, in all probability; at all events when they consist largely of " nebulous "matter; and the nebulæ probably must take stand as yet more juvenile. Each nebula may be not one Sun only in the making," but a whole system or Universe of stars in embryo.

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Both the clusters and the nebulæ as seen by us are of many different shapes. It does not follow that, if we could approach billions of miles nearer, we should see them in precisely the same shapes.

Some "clusters" are globular in outline; and these are believed to be extremely rapid in movement, travelling through Space at a speed of about ninety miles each second. But they are completely outdone by some of the nebula-the "spiral" kind-which have been reckoned to hurry on their distant travels at an average rate of two hundred and forty miles a second.

One marked difference between stars and nebulæ