ent densities; others are of the nature of eruptive rocks; others partake of metamorphic character; others are brecciaform. And it is reasonable to conclude that these various formations have belonged to a globe in which they occurred in some sort of geological order. In the centre, by inference from facts observed on the earth, there would be a dense nucleus composed of the metal which we call 'meteoric iron;' upon this would be superposed the less dense granular metallic strata, which are exemplified in many characteristic meteorites; then the strata of stony character with but little metal in them; and lastly, the rocks which are absolutely without metal. Of each of all these we have specimens that have fallen from the sky.

But supposing meteorites to be the débris of a demolished globe, we are brought face to face with the question, how did the globe become disintegrated? They who have ascribed the existence of multitudes of minute planetary bodies to the rupture of a great one have generally ascribed that rupture to accidental causes. This is. however, an unsatisfactory, because unphilosophical, treatment of the question; for what in nature is accidental? Some unfortuitous cause must be sought for the dissolution; some process in harmony with the unison of natural phenomena. Is there any tendency to breaking-up in those planets which we can examine with comparative closeness? We look to our earth first for a reply. And surely enough we see what may be taken for the commencement of a disruptive process. Its crust is cracked in all directions; everywhere we find what the geologist calls faults,' which are ascribable to an effort of the crust to accommodate itself to a change of volume of the igneous mass beneath it. It is reasonable to suppose that the fluid or viscous nucleus of our globe will, in its solidifying process, behave in accordance with the observed law of behaviour of solidifying materials, and temporarily expand, bulging the crust outwards for a time. And after this expansion, a contraction, consequent upon cooling, would ensue, and the crust would sink in upon the retreating nucleus, and crush and crumble itself into accommodation with the smaller space it would have to occupy. We do not see great cracks on the earth because of the filling-up action of its air and water; but if we turn from the earth to the moon, which has neither atmosphere nor water, we shall find by careful telescopic search that her outer crust is scored with hundreds of gaping crevices, that run for miles through mountain, valley, and plain. These cracks are of vast length; they are about a mile. wide, and of depth unknown. Their origin is almost plainly told by their aspect. It seems obvious that many of them are flaws produced either by a contraction of the crust or by the thrust of some expanding matter underneath it. Whatever the cause, the fact is plain that the moon is cracking; and if we could place the same confidence in the revelations of ancient as of modern telescopes, we

should be justified in assuming that the disruption is on the increase, for there are vastly more of these cracks known now than were recorded by the observers of a few generations back.

If it be true that the lunar fissures are extending and deepening, we have evidence of a planet in a state of dissolution; for in course of ages beyond our conception, perhaps, but still comprising a period that is short in comparison with many that astronomers are called upon to assign to some cosmical occurrences-in the course of ages, the lunar globe must be split up into a mass of detached blocks, which, if they be not all of the same size and density, will slide upon and chafe one another, separate little by little from the parent проп mass, and scatter themselves about the orbit which the moon has described. A zone of these disjecta membra would thus be formed around the earth, and it is conceivable that conditions may arise which would result in the occasional attraction of some of them to the earth, and their precipitation as actual meteorites thereupon.

In this way we are led to regard meteorites as the last phase of a planetary development, for they come to us as waifs from the wreck of a world. The steps of this evolution may be taken as represented by the sun, which is a planet in the state of fiery formation; by the earth, which is a planet in its matured phase (and we may regard maturity as the state of fitness for life), with its fire subdued; by the moon, which is a dead decaying planet; and by the meteorites, which are the results of that decay. But the question arises, do these meteorites possess any re-creative power? have they anything analogous to life in them? To this we briefly reply that they will have motion, and motion is mechanical life. It is quite in accordance with modern scientific evidence to assert the possibility of a planet being produced by the clashing of meteoric masses; indeed, one favourite theory of the maintenance of the sun's heat and light is, that the raining of meteors upon his surface keeps up the supply of heat by the well-known conversion into that element of the meteors' vis viva of motion: for it is an axiom that motion arrested becomes heat.

To return to M. Meunier. One deduction has led him to seek others, and having reasoned that meteorites are the débris of a planet, he tries to discover what was the position of that planet in the universe: was it attached to our solar system, or do its remnants reach us from the depths of space? In considering this question, it must be remarked that there are two opinions concerning the nature of the meteorites that fall to the earth. According to one, they are bodies of the same class as the luminous meteors or falling stars,' of which we have lately had several interesting displays. According to another, they are a totally independent class of bodies. From the little that can be made of the study of the light of falling stars, it is concluded that they are of a low specific gravity and kindle with a gas

like flame. They are, too, proved to be in some relation allied to comets, which we know to be extremely tenuious bodies. And comets come to us from the depths of space with the meteors in their trail.

Now the meteorites are very dense, they are of stony and metallic character, and it seems improper to connect them with the extremely light bodies just mentioned. They are in their constitution planetary; their very materials are earthly and metallic substances common to our globe. Their density shows them to be related substantially to the planets near to the sun. If we look at a table exhibiting the densities of the planets, we shall see that the three nearest, namely, Mercury, Venus, and the Earth, are all about six times as dense as water, Mars is about four times as dense, and Jupiter, Saturn, Uranus, and Neptune have on the average just the same density as water. The moon, our satellite, is about three and a half times as dense, or most nearly equal to Mars. The density or compactness diminishes as we depart from the sun. Now the average density of the meteorites is about three times that of water, or approximately that of the moon or Mars; and this fact, combined with some considerations depending upon the probably relative age of the members of our system, leads M. Meunier to the conclusion that the primitive globe that was split up into meteorites was either a small satellite of the earth-another moon in fact-or a planet exterior to Mars, perhaps related to the zone of planetoids which we know to exist there, and which were regarded by Olbers as the fragments of a planet that once existed there as a whole. In view, however, of the comparatively few meteoric stones which fall to the earth, it is conceivable that the planet which furnished them was a small one; and from the want of periodicity in their fall-for they appear to come with no regularity-it is argued by our hypothesist that the store from which we receive them is near to the earth. And thus it is maintained that they are the remains of a second moon that once accompanied our earth, but that ages ago crumbled to decay. That the earth has not always received this meteoric pelting is suggested by the rarity with which meteoric masses are found in any but the most recent geological formations. And if the store of meteorites from this source is small, the time must come when it will be exhausted and no more will fall. But then, if these speculations have any foundation, the supply will one day, in æons to come, be renewed, and that at the expense of our existing moon.

Such is a brief and imperfect sketch of a curious chain of deduction. In bringing it within range of popular perception, we by no means pledge ourselves to its entire validity. There are some weak points in M. Meunier's reasoning, but this is not the place to discuss them. It is, however, the place to record what is curious and interesting, and at least M. Meunier's catenation of possibilities deserves these qualifications. J. CARPENTER, F.R.A.S.