All the substances which we are accustomed to see and handle in our daily lives belong to our world. There are vegetables which grow in the earth, minerals which are dug out of it, and elementary things, such as air and water, which have always made up a part of this planet since man knew it. These are obvious, but there are other things not quite so obvious which also help to form our world. Among these we may class all the elements known to chemists, many of which have difficult names, such as oxygen and hydrogen. These two are the elements which make up water, and oxygen is an important element in air, which has nitrogen in it too. There are numbers and numbers of other elements perfectly familiar to chemists, of which many people never even hear the names. We live in the midst of these things, and we take them for granted and pay little attention to them; but when we begin to learn about other worlds we at once want to know if these substances and elements which enter so largely into our daily lives are to be found elsewhere in the universe or are quite peculiar to our own world. This question might be answered in several ways, but one of the most practical tests would be if we could get hold of something which had not been always on the earth, but had fallen upon it from space. Then, if this body were made up of elements corresponding with those we find here, we might judge that these elements are very generally diffused throughout the bodies in the solar system.

It sounds in the highest degree improbable that anything should come hurling through the air and alight on our little planet, which we know is a mere speck in a great ocean of space; but we must not forget that the power of gravity increases the chances greatly, for anything coming within a certain range of the earth, anything small enough, that is, and not travelling at too great a pace, is bound to fall on to it. And, however improbable it seems, it is undoubtedly true that masses of matter do crash down upon the earth from time to time, and these are called meteorites. When we think of the great expanse of the oceans, of the ice round the poles, and of the desert wastes, we know that for every one of such bodies seen to fall many more must have fallen unseen by any human being. Meteors large enough to reach the earth are not very frequent, which is perhaps as well, and as yet there is no record of anyone's having been killed by them. Most of them consist of masses of stone, and a few are of iron, while various substances resembling those that we know here have been found in them. Chemists in analyzing them have also come across certain elements so far unknown upon earth, though of course there is no saying that these may not exist at depths to which man has not penetrated.

A really large meteor is a grand sight. If it is seen at night it appears as a red star, growing rapidly bigger and leaving a trail of luminous vapour behind as it passes across the sky. In the daytime this vapour looks like a cloud. As the meteor hurls itself along there may be a deep continuous roar, ending in one supreme explosion, or perhaps in several explosions, and finally the meteor may come to the earth in one mass, with a force so great that it buries itself some feet deep in the soil, or it may burst into numbers of tiny fragments, which are scattered over a large area. When a meteor is found soon after its fall it is very hot, and all its surface has 'run,' having been fused by heat. The heat is caused by the friction of our atmosphere. The meteor gets entangled in the atmosphere, and, being drawn by the attraction of the earth, dashes through it. Part of the energy of its motion is turned to heat, which grows greater and greater as the denser air nearer to the earth is encountered; so that in time all the surface of the meteor runs like liquid, and this liquid, rising to a still higher temperature, is blown off in vapour, leaving a new surface exposed. The vapour makes the trail of fire or cloud seen to follow the meteor. If the process went on for long the meteor would be all dissipated in vapour, and in any case it must reach the earth considerably reduced in size.

Numbers and numbers of comparatively small ones disappear, and for every one that manages to come to earth there must be hundreds seen only as shooting stars, which vanish and 'leave not a wrack behind.' When a meteor is seen to fall it is traced, and, whenever possible, it is found and placed in a museum. Men have sometimes come across large masses of stone and iron with their surfaces fused with heat. These are in every way like the recognized meteorites, except that no eye has noted their advent. As there can be no reasonable doubt that they are of the same origin as the others, they too are collected and placed in museums, and in any large museum you would be able to see both kinds—those which have been seen to come to earth and those which have been found accidentally.

The meteors which appear very brilliant in their course across the sky are sometimes called fire-balls, which is only another name for the same thing. Some of these are brighter than the full moon, so bright that they cause objects on earth to cast a shadow. In 1803 a fiery ball was noticed above a small town in Normandy; it burst and scattered stones far and wide, but luckily no one was hurt. The largest meteorites that have been found on the earth are a ton or more in weight; others are mere stones; and others again just dust that floats about in the atmosphere before gently settling. Of course, meteors of this last kind could not be seen to fall like the larger ones, yet they do fall in such numbers that calculations have been made showing that the earth must catch about a hundred millions of meteors daily, having altogether a total weight of about a hundred tons. This sounds enormous, but compared with the weight of the earth it is very small indeed.

Now that we have arrived at the fact that strange bodies do come hurtling down upon us out of space, and that we can actually handle and examine them, the next question is, Where do they come from? At one time it was thought that they were fragments which had been flung off by the earth herself when she was subject to violent explosions, and that they had been thrown far enough to resist the impulse to drop down upon her again, and had been circling round the sun ever since, until the earth came in contact with them again and they had fallen back upon her. It is not difficult to imagine a force which would be powerful enough to achieve the feat of speeding something off at such a velocity that it passed beyond the earth's power to pull it back, but nothing that we have on earth would be nearly strong enough to achieve such a feat. Imaginative writers have pictured a projectile hurled from a cannon's mouth with such tremendous force that it not only passed beyond the range of the earth's power to pull it back, but so that it fell within the influence of the moon and was precipitated on to her surface! Such things must remain achievements in imagination only; it is not possible for them to be carried out. Other ideas as to the origin of meteors were that they had been expelled from the moon or from the sun. It would need a much less force to send a projectile away from the moon than from the earth on account of its smaller size and less density, but the distance from the earth to the moon is not very great, and any projectile hurled forth from the moon would cross it in a comparatively short time. Therefore if the meteorites come from the moon, the moon must be expelling them still, and we might expect to see some evidence of it; but we know that the moon is a dead world, so this explanation is not possible. The sun, for its part, is torn by such gigantic disturbances that, notwithstanding its vast size, there is no doubt sufficient force there to send meteors even so far as the earth, but the chances of their encountering the earth would be small. Both these theories are now discarded. It is believed that the meteors are merely lesser fragments of the same kind of materials as the planets, circling independently round the sun; and a proof of this is that far more meteorites fall on that part of the earth which is facing forward in its journey than on that behind, and this is what we should expect if the meteors were scattered independently through space and it was by reason of our movements that we came in contact with them. There is no need to explain this further. Everyone knows that in cycling or driving along a road where there is a good deal of traffic both ways the people we meet are more in number than those who overtake us, and the same result would follow with the meteors; that is to say, in travelling through space where they were fairly evenly distributed we should meet more than we should be overtaken by.

You remember that it was suggested the sun's fuel might be obtained from meteors, and this was proved to be not possible, even though there are no doubt unknown millions of these strange bodies circling throughout the solar system.

There are so many names for these flashing bodies that we may get a little confused: when they are seen in the sky they are meteors, or fire-balls; when they reach the earth they are called meteorites, and also aerolites. Then there is another class of the same bodies called shooting stars, and these are in reality only meteors on a smaller scale; but there ought to be no confusion in our thoughts, for all these objects are small bodies travelling round the sun, and caught by the earth's influence.

When you watch the sky for some time on a clear night, you will seldom fail to see at least one star flash out suddenly in a path of thrilling light and disappear, and you cannot be certain whether that star had been shining in the sky a minute before, or if it had appeared suddenly only in order to go out. The last idea is right. We must get rid at once of the notion that it would be possible for any fixed star to behave in this manner. To begin with, the fixed stars are many of them actually travelling at a great velocity at present, yet so immeasurably distant are they that their movement makes no perceptible difference to us. For one of them to appear to dash across the heavens as a meteor does would mean a velocity entirely unknown to us, even comparing it with the speed of light. No, these shooting stars are not stars at all, though they were so named, long before the real motions of the fixed stars were even dimly guessed at. As we have seen, they belong to the same class as meteors.

I remember being told by a clergyman, years ago, that one night in November he had gone up to bed very late, and as he pulled up his blind to look at the sky, to his amazement he saw a perfect hail of shooting stars, some appearing every minute, and all darting in vivid trails of light, longer or shorter, though all seemed to come from one point. So marvellous was the sight that he dashed across the village street, unlocked the church door, and himself pulled the bell with all his might. The people in that quiet country village had long been in bed, but they huddled on their clothes and ran out of their pretty thatched cottages, thinking there must be a great fire, and when they saw the wonder in the sky they were amazed and cried out that the world must be coming to an end. The clergyman knew better than that, and was able to reassure them, and tell them he had only taken the most effectual means of waking them so that they might not miss the display, for he was sure as long as they lived they would never see such another sight. A star shower of this kind is certainly well worth getting up to see, but though uncommon it is not unique. There are many records of such showers having occurred in times gone by, and when men put together and examined the records they found that the showers came at regular intervals. For instance, every year about the same time in November there is a star shower, not comparable, it is true, with the brilliant one the clergyman saw, but still noticeable, for more shooting stars are seen then than at other times, and once in every thirty-three years there is a specially fine one. It happened in fact to be one of these that the village people were wakened up to see.

Not all at once, but gradually, the mystery of these shower displays was solved. It was realized that the meteors need not necessarily come from one fixed place in the sky because they seemed to us to do so, for that was only an effect of perspective. If you were looking down a long, perfectly straight avenue of tree-trunks, the avenue would seem to close in, to get narrower and narrower at the far end until it became a point; but it would not really do so, for you would know that the trees at the far end were just the same distance from each other as those between which you were standing. Now, two meteors starting from the same direction at a distance from each other, and keeping parallel, would seem to us to start from a point and to open out wider and wider as they approached, but they would not really do so; it would only be, as in the case of the avenue, an effect of perspective. If a great many meteors did the same thing, they would appear to us all to start from one point, whereas really they would be on parallel lines, only as they rushed to meet us or we rushed to meet them this effect would be produced. Therefore the first discovery was that these meteors were thousands and thousands of little bodies travelling in lines parallel to each other, like a swarm of little planets. To judge that their path was not a straight line but a circle or ellipse was the next step, and this was found to be the case. From taking exact measurements of their paths in the sky an astronomer computed they were really travelling round the sun in a lengthened orbit, an ellipse more like a comet's orbit than that of a planet. But next came the puzzling question, Why did the earth apparently hit them every year to some extent, and once in thirty-three years seem to run right into the middle of them? This also was answered. One has only to imagine a swarm of such meteors at first hastening busily along their orbit, a great cluster all together, then, by the near neighbourhood of some planet, or by some other disturbing causes, being drawn out, leaving stragglers lagging behind, until at last there might be some all round the path, but only thinly scattered, while the busy, important cluster that formed the nucleus was still much thicker than any other part. Now, if the orbit that the meteors followed cut the orbit or path of the earth at one point, then every time the earth came to what we may call the level crossing she must run into some of the stragglers, and if the chief part of the swarm took thirty-three years to get round, then once in about thirty-three years the earth must strike right into it. This would account for the wonderful display. So long drawn-out is the thickest part of the swarm that it takes a year to pass the points at the level crossing. If the earth strikes it near the front one year, she may come right round in time to strike into the rear part of the swarm next year, so that we may get fine displays two years running about every thirty-three years. The last time we passed through the swarm was in 1899, and then the show was very disappointing. Here in England thick clouds prevented our seeing much, and there will not be another chance for us to see it at its best until 1932.

These November meteors are called Leonids, because they seem to come from a group of stars named Leo, and though the most noticeable they are not the only ones. A shower of the same kind occurs in August too, but the August meteors, called Perseids, because they seem to come from Perseus, revolve in an orbit which takes a hundred and forty-two years to traverse! So that only every one hundred and forty-second year could we hope to see a good display. When all these facts had been gathered up, it seemed without doubt that certain groups of meteors travelled in company along an elliptical orbit. But there remained still something more—a bold and ingenious theory to be advanced. It was found that a comet, a small one, only to be seen with the telescope, revolved in exactly the same orbit as the November meteors, and another one, larger, in exactly the same orbit as the August ones; hence it could hardly be doubted that comets and meteors had some connection with each other, though what that connection is exactly no one knows. Anyway, we can have no shadow of doubt when we find the comet following a marked path, and the meteors pursuing the same path in his wake, that the two have some mysterious affinity. There are other smaller showers besides these of November and August, and a remarkable fact is known about one of them. This particular stream was found to be connected with a comet named Biela's Comet, that had been many times observed, and which returned about every seven years to the sun. After it had been seen several times, this astonishing comet split in two and appeared as two comets, both of which returned at the end of the next seven years. But on the next two occasions when they were expected they never came at all, and the third time there came instead a fine display of shooting stars, so it really seemed as if these meteors must be the fragments of the lost comet.

It is very curious and interesting to notice that in these star showers there is no certain record of any large meteorite reaching the earth; they seem to be made up of such small bodies that they are all dissipated in vapour as they traverse our air.