would prove nothing about the origin of comets and meteors. To say that they came from out the interstellar depths on hyperbolic paths, is to assert what can be disproved by mathematical demonstration. But if it could be proved, what would it amount to? Merely to this—that comets which now travel on closed paths once travelled on endless paths. We are no whit nearer the explanation of their origin. If the interstellar depths are crowded with meteor flights, we have to ask whence the meteor flights came. To say that fish which have been drawn from the sea were originally swimming about in the sea, is surely not to add much to our knowledge about fish.

It may be urged, however, that comets and meteor-streams are simply the material left unused after the various solar systems in our galaxy had been formed, by processes of meteoric aggregation.

Unfortunately for this explanation, the comets and meteor systems we have to explain are precisely those which, had they existed from the earlier ages, when our solar system and its fellows were forming, would have been the first to be gathered up. For they are those which pass near the orbits of various planets, some near the orbit of Jupiter, some near that of Saturn, or of Uranus, or of Neptune, and about four hundred which pass near the orbit of our earth. These comets, with their associated meteor systems, would have had less chance of escape than any others, during the millions of years belonging to the formative processes of our solar system. Yet those are precisely the comets and meteor systems which we chiefly need to interpret.

Suppose that, instead of making mere guesses, we consider actual facts, and open our eyes to the views suggested by them.

I take first the millions of meteors encountered by the earth each year, and the hundreds of earth-crossing meteor systems already recognised. Taking for our guide proposition (1), we are led to the conclusion that in remote ages there were hundreds, if not thousands, of comets whose tracks crossed the track of the earth, or at any rate approached very near to it. That some of these comets thus crossed the earth's track casually, that is through mere chance coincidence, we may well believe. Nay, this is known, as will presently be seen. But if all did, then must there have been millions of millions of comets in remote times, to account for so many chancing to cross the earth's track;-with this startling circumstance to be considered in addition, that ninety-nine out of a hundred of those whose paths did not cross the earth's track have entirely disappeared, while a considerable proportion of those which do cross that track (and which, therefore, have been exposed for millions of years to an extra risk of destruction) remain.

This idea we may safely reject. But if we do, then we have to account for a special earth-crossing family of comets and meteorstreams, without going outside to look for the origin of such bodies; for the moment we go outside we encounter the difficulty which has just driven us from any merely casual interpretation.

In other words, we must look to the earth herself to explain the great majority of these earth-crossing systems.

In this way Meunier and Tschermak were driven to look to the earth herself for the origin of meteorites. Proposition (3) above enables us to extend their reasoning, specially directed to particular classes of aerolites, to all classes of such bodies, to all meteors, down even to the tiniest falling star, only visible perhaps in the field of a powerful telescope. Not all these bodies, but a goodly proportion, must have been generated in some specially terrene manner.

We have actually no possible way of explaining the terrestrial origin of any meteors but in volcanic outbursts. Moreover, we are obliged to set the time when such outbursts took place very far back in the past, seeing that at present the volcanic forces of the earth, even as manifested at Krakatoa recently, possess nothing like the power necessary for the ejection of matter beyond the range of the earth's back-drawing power. Looking, however, at the immense extrusive power of the volcanoes of the tertiary era, when basaltic lava covering hundreds of thousands of square miles to a depth of from 1,000 to 14,000 feet were poured forth, we can conceive the still mightier energies of volcanoes in the secondary era, their still more tremendous power in the primary era, and so, passing backwards to millions of years beyond the first beginnings of life on the earth, we can even picture to ourselves volcanoes ejecting matter with velocities of ten or twelve miles per second. With such velocities flights of ejected particles would pass beyond the earth's attraction, and if she were the only body in the universe, such ejected matter would travel away from her never to return.

But, although such expelled bodies would never return to the earth, they would not escape from the solar system. To drive them for ever away from her, the earth would have to impart a much larger velocity-an average of about twenty-six miles per second. The greater number of the expelled bodies would travel thenceforth on an orbit round the sun, crossing the earth's track at or near the place where they were first sent forth from their parent planet.

One may almost say that this origin of many meteorites and meteor systems is forced upon us by the evidence. Still it would be negatived if we found that volcanoes do not eject matter at all resembling meteorites in structure. The reverse, however, is the case. Ranging the products of volcanic ejection in order according to the amount of iron they contain, and ranging meteorites in like manner, we find the two series coinciding over the greater portion of the longer-the volcanic series. We might not indeed have known how closely the most ferruginous volcanic products resemble the iron meteorites in structure but for the accident that Nordenskjold discovered a mass which he mistook for an iron meteorite, but which is found now to be really a volcanic ejection, akin in structure to the VOL. XIX.-No. 111. 3 A

field of basaltic lava (at Ovifak on the shores of Greenland), in the midst of which it had fallen while the lava was still plastic to retain this missile as it fell after its flight through many miles of air.

We may, therefore, regard the terrestrial origin of many meteorites as highly probable, if not in effect demonstrated.

Here Tschermak and Meunier pause, as also does Ball, who thus far had followed them. The last named does not even ask, in that singularly interrogative and irresponsive work the Story of the Heavens, whether we may not go further.

For my own part I find in this result the first step in a most interesting and suggestive path of inquiry.

Regarding a large proportion of the material visitants of the earth as originally earthborn, we may conclude that in the remote time when our earth was a baby world, sunlike in condition, her path was traversed by hundreds of comets, her own progeny. These comets were followed severally by their trains of meteoric attendants. They were exposed to the action of those solar forces by which, within the last half-century, a once promising member of another comet family became dissipated until it finally lost altogether its cometic character. Millions of years ago, probably, every one of them had been thus broken up until nothing remained but the streams of meteoric bodies, travelling round the orbit which had once been that of the earthejected comet.

But this being the case with the earth, was the case also no doubt with every planet. Even our little moon, whose scarred face still shows signs of the volcanic energies she once possessed, played her part in giving birth to such comets as she was equal to. If she possessed less volcanic power than the earth (at the same stage of the life of each), she required less power to eject matter for ever from her interior. On the other hand, the giant planets required greater power; but then they also possessed it. If Jupiter, for example, required power enough to eject bodies with a velocity of forty or fifty miles per second, yet it must be remembered that he is 310 times as massive, and therefore 310 times as strong as our earth. (For matter, 'inert matter' as many choose to call it, measures in reality the strength of the orbs in space, and not only possesses power, but a power acting so swiftly across vast distances that the velocity of light is rest by comparison. Moreover, this power possessed by 'inert' matter is the source of every form of energy of which we know, even of life itself.) So with the other giant planets.

Jupiter, then, and each one of his giant brethren, must during its sunlike stage have possessed the comet-ejecting power. Each giant planet must have had its comet family, at that remote time in the history of the solar system. And the comets thus formed by the giant planets, while no doubt very numerous, must, many of them, have been far more important than those to which our earth gave

birth. Those comets would have lasted much longer, before dissipation due to solar disturbances set in. Then, also, the sunlike state of the giant planets must have lasted long after the earth and all the terrestrial planets had passed that stage. For being so much larger, the giant planets must have longer lives-the stages of planetary life being in effect stages of cooling. In fact, there are clear signs that neither Jupiter nor Saturn has cooled down to the earth's condition; each is still too hot for the waters of its future seas to rest on its fiery surface. On this account also, then, we might expect to find that some comets, sprung from giant planets and forming their families, might have remained even to the present time.

Turning to the solar system, we find that this actually is the case. Nay, I myself, long before I had the least thought of attributing comets to planetary eruptive energies, had described the comets which hang about the orbits of the giant planets as 'The comet families of the giant planets.' Some of the members of these families are among those from which the association between meteors and comets came first to be known. For instance, the meteors of November 13-14 (the Leonides) are associated with a comet depending on the orbit of Uranus; and the meteors of November 27-28 are associated with a comet depending on the orbit of JupiterBiela's famous comet.

Of course the members of these comet families are exceedingly old. How old they are we cannot tell; but that they are very old indeed is shown by the way in which, while they are unmistakably associated with the paths of the several giant planets, their orbits yet diverge far enough from those of their respective planet parents to indicate hundreds of thousands of years of perturbing action, unless indeed in some cases we may suppose that not the slow perturbing action of bodies at a distance, but the very active influence of some orb coming very close to a comet may have shifted the comet's path. So many of their orbits pass through the widely spread zone of asteroids, that we may very well imagine occasional very close approach to one or other of these bodies, and consequently a considerable change of orbit. It was thus that Sir John Herschel for a time tried to explain the disappearance of Biela's comet; may it not,' he said, have got entangled in the zone of asteroids, and have had its course altered by the influence of one of these bodies?'

Encouraged by the confirmation of the expulsion theory of comets, which we have found at this our first step, may we not boldly proceed yet one step further?

The stars, like the giant planets, should have their part to play— a grander part of course-in the world of comet expulsion. They differ only from the giant planets, nay from the earth herself, in being in a different part of their orb life. It is probable, indeed, that among the stars there are orbs differing much less from Jupiter or

Saturn than either of these still hot and fiery planets differs from the earth. Of course an orb like our sun, the one star we are able to examine, will require much greater energy to expel from his interior a flight of bodies, to become presently a flight of meteors or a comet, than would a planet even of the giant type. Our sun, for example, would have to impart a velocity of 382 miles per second to a body ejected from his interior, that that body should pass away from his control for ever. But the sun possesses the required power. His mass, and therefore his might, exceeds that of the earth more than 320,000 times, that even of Jupiter 1,048 times.

is

We have no means of recognising by its orbital motion a starexpelled comet or meteor flight. But we need not seek for bodies to tell us of expulsion, ages on ages ago. The stars are now in their sunlike state. They must therefore be doing such work now, if there any truth in the theory to which we have been led. Now there is one of the stars which is near enough to be asked whether it really possesses and uses such expulsive power-our own sun. His answer is unmistakable. In 1872 and at sundry times since, he has been caught in the act of ejecting bodies, probably liquid or solid, through the hydrogen atmosphere around his globe, with velocities so great that the matter thus expelled from his interior can never return to him the velocities ranging to 450 miles per second at the least. What he is doing now he has doubtless done for millions, nay for tens of millions, of years in the past. What he has thus done, his fellowsuns the stars, thousands (if not millions) of millions in number, have doubtless done also. Uncounted billions then of ejected meteor flights or comets must be travelling through interstellar spaces, visiting system after system, flitting from sun to sun, in periods to be measured by millions of years.

The answer then to the question, Whence came the comets ? would appear to be:—

(1) Comets which visit our system from without were expelled millions of years ago from the interior of suns.

(2) Comets which belong to our system were mostly expelled from the interior of a giant planet in the sunlike state, but a small proportion may have been captured from without.

(3) The comets of whose past existence meteor-streams tell us were for the most part expelled from our earth herself when she was in the sunlike state, but some of the more important were expelled from the giant planets, and a few may have been expelled from

suns.

RICHARD A. PROCTOR.