The interest divides itself into three subjects, viz., the nature of the material, its form, and the appearance and condition of the surface and of the interior of the mass.

A large proportion of the specimens are of a curious mixture of iron, nickel, and other metals, frequently regarded as peculiar to meteorites in whatever the part of the world they have fallen, or whatever interval has elapsed since their fall. The other specimens are chiefly fragments, some containing scarcely a trace of iron, and others a little iron, but most of them consisting of either felspathic or silicious sand, cemented together rather loosely. The appearance is extremely similar to that attained by sand after very long exposure in a furnace. The sand is compacted into a sandstone, but the grains are very imperfectly cemented. The outside of these specimens is almost without exception black, and has every appearance of having been fused. The size of the block is various; some are pebbles, not much larger than a walnut, others are as large as a man's head; some are broken fragments. One of them is very curious, as it exhibits distinctly the cause of the smooth surface. That side of the pebble which met the air (the part that is in the direction of progress) in the rapid transit of the stone through the air, is perfectly glazed, and the glaze has run over the edge; the rest, however, is only slightly glazed.

The surface of the metallic meteorites is especially remarkable, and there are many cases in which the crystalline form can not only be recognized as an outline, but may even be measured. The usual shape of the crystals is the octahedral. In some the outside is a mass of crystals of moderate size, greatly rounded, but still recognizable. These are the larger specimens. In others of smaller size the form is more distinct and less altered by weathering. Some, however, are completely rounded externally, and give no appearance of crystallization until broken. One specimen of large size has been partly sawn and then broken. The fracture in this case marks, in the most striking manner, the crystalline state of the mass, as it gives a repetition of parallel faces along the whole length of the broken part, amounting to five inches.

The external form of the non-metallic meteorites offers nothing very remarkable, beyond the fact of the peculiar rounded surface, apparently caused by great friction—a friction which can only be due to the passage of the mass through the air at an extremely rapid pace. The internal fracture differs nothing from that of a lump of similar material on the earth. The melting that has taken place at the surface, resulting in a deep brown or black glaze, is of no great thickness, and is strictly superficial.

The internal structure of the metallic masses is curious in
VOL. IV.-NO. III.

N

many ways, and the peculiar markings, caused apparently by the crystalline condition of the metal, are often very beautifully shown by irregular oxidation. Some specimens are covered with lines, parallel, and crossing each other with extreme regularity, resulting in a beautiful pattern. Others are less regular, but equally beautiful. Many have smooth blebs in the interior, hollow spaces once filled with pyrites which have fallen or decomposed out, leaving a perfectly smooth cavity. In some, real stones or foreign substances, more or less different from the mass of the meteorite, are buried within the mass; some are enclosed, and show from their angular surface how completely foreign they must have been; others are only partially buried, portions of them being outside. It is difficult to conceive how these may have been packed into their places.

One of the most singular of the specimens is part of a stone that fell at Tula, in Russia, in 1846. The crystalline structure was first observed in polishing a part of this specimen, which weighs 71 lbs. The original mass weighed 542 lbs.

The stones have sometimes fallen in showers. This was the case in France with some of those that have no metal, but consist almost entirely of felspathic stone. In the national museum at Prague are several large meteorites, one of which is a stone seen to fall. It is entirely melted on one side, and unchanged on the other. The melted side is quite round and smooth, and is black to the thickness of about one-sixteenth of an inch.

The various facts above stated are but a few out of a rich variety in reference to this curious subject, but they are sufficient to suggest some considerations as to their meaning, and also as to their bearing on the condition of those vast spaces that occur between the recognized and known bodies that make up our planetary system. It is an idea, not a little startling, when first presented, that besides the planets long known, and those distant ones recently discovered, and scarcely visible to the naked eye; besides those numerous asteroids or minute planets, almost all discovered during the present century, but whose number is constantly increasing, and will soon perhaps mount to a hundred; besides the satellites, which are much more numerous than was once thought; besides those wandering comets, sometimes whirling with incredible rapidity close to the sun, and then passing off for centuries or even thousands of years, lazily traversing space as they cross the orbits of the various planets, and sometimes reaching the outskirts of our system, far beyond the most distant known planet;-that besides all these, there are also belts consisting of numberless smaller fragments of matter, some metallic, others earthy, and only made evident to our senses when by some chance they enter

within the limits of our atmosphere, or when we approach so near them that they suddenly become incandescent, and glow with intense brilliancy for a few brief seconds.

There is hardly any rational way of escaping from this conclusion, that all space must be as thickly peopled with these fragments as is the air in a room with particles of dust. When the rays of the sun shine in through a narrow chink, all these minute particles in the course of a ray are made evident, and so these atoms of the dust of space are from time to time seen, not indeed when the sun is shining, but when in the dark but clear nights we watch the heavens, and note all the shining points that shoot out from the blue vault, and seem to disappear as they came. Probably, in the majority of cases, where there is merely this momentary line of brilliant light, the atom has been made bright by the friction produced, and heat evolved in passing through the thin air overhead. Heated intensely, the whole has become dissipated, being either broken up or oxidized into particles quite invisible. In other cases, where the magnitude is greater, the time longer, and the phenomena more marked, a sensible mass of matter is caught up, and though attracted by the earth and approaching its surface, yet fails to reach it, being also broken up into minute fragments of dust by the enormous friction met with before it can reach the actual land and sea. That in their course downwards these masses are occasionally swayed about, taking a zigzag or irregular path, seems certain, and now and then the actual broken fragments are seen to approach the earth, though they cannot be picked up on the spot where they appeared to fall. Now and then, however, a giant appears-a Triton among these minnows of the sky; molten on the surface by the friction, it yet succeeds in retaining its natural state, until at last it falls to the earth a solid, though rarely in an unbroken state. Masses of magnetic iron and nickel, with occasionally other metals, masses of sandstone, mixed masses of metal and sandstone, have all been picked up on the earth after falling from the sky, and have been examined by competent chemists. They are the materials that people space; they are fragments of matter widely, and perhaps universally, distributed; they are materials collected or left behind by the wild comets in their course; they may be the food of the sun, the fuel conveyed in some mysterious manner to keep up that vast burning mass that is the source of light and heat, whose rays give life, and of whose atmosphere we are now beginning to learn something from the experiments recently made on light. And these materials accord pretty well with those common on the earth. They afford no new metal or mineral. They are combinations not unknown, if not common, of very familiar ingredients.

That our whole solar system is occupied more or less thickly by particles of matter of the same kind; that these are collected into masses, varying in size from the dust that no microscope can render visible, to the huge planet Jupiter, and the sun itself, compared with which all the known solid bodies of our system are as nothing; that all these parts to our system are mutually dependent, working together and performing some useful purpose; that there are abundant means by which waste can be supplied and a perfect balance constantly preserved;-all this is so perfectly consistent with what we know generally of the course of nature, and the good providence that has ordered all things, that the idea commends itself to our experience and would be accepted at once by most of us. But if it is so, if really this is the explanation of the phenomena of meteors, fireballs, falling stars and aërolites; if these are but the dust of our system, they yet seem to follow some definite law, not unlike that which governs our own movements round the sun. Crossing as we do the direction of this strange pell-mell of waste material chiefly at certain periods of the year, it would seem that it is a belt having definite boundaries; but as, on the other hand, though it is on special days that the phenomena are chiefly recognized, there are few nights of the year in which there are not some, there must either be many other such belts constantly crossed, or, which is more probable, all space is thus partially occupied, although there are certain limited and definite groups revolving in an orbit round the central mass of the sun.

But finally, if our own solar system is thus made up, why should not others be so? Why should not whole systems consist of matter less collected into large globes, and more spread in fragments; and why should not some or all of them be self luminous? Such a state of matter might well produce the anomalous appearances presented by unresolved nebulæ, and they would even accord pretty well with the most recent observations on many groups of what has already been called star-dust. It may be wild and fanciful to dream of possible explanations; but where, as in these celestial phenomena, the actual facts are so few, who can help speculating from even the least proved analogies, if they seem to afford a rational clue?

There is no department of science more fascinating than the discussion of these physical problems. But they must not induce us to believe that astronomy can be studied by thus revelling in fanciful dreams of celestial possibilities. They are not without interest, but this is not to be estimated at more than its real value.

THE USE OF LOW POWERS WITH DEEP EYE

PIECES.

BY HENRY J. SLACK, F.G.S.,

Member of the Microscopical Society of London.

IF I may judge from the practice of those microscopists with whom I am personally acquainted, and from the best works on the subject of microscopic manipulation, it would appear that sufficient attention has not been paid to the circumstances under which magnification is best obtained by the employment of low objectives and deep eye-pieces; nor has the power of eyepieces been as yet brought up to the highest point of practical usefulness by microscope-makers.

In the Micrographic Dictionary all that I notice upon eyepieces occurs in the introduction, at the bottom of p. xvii. (second edition), and runs as follows:-"Always one, and sometimes two eye-pieces are obtained with the microscope; but the highest eye-piece which is made should always be procured, for although high eye-pieces are so far objectionable that they magnify the imperfections formed by the object-glass as well as the image itself, yet they frequently render parts of structure distinct which are perhaps only just perceptible with a lower eye-piece." This passage shows that the able authors of the Micrographic Dictionary merely regarded an increase in the power of the eye-piece as a substitute, of a make-shift kind, for an augmentation in the power of the objective. In the valuable lectures of Mr. Lionel Beale, entitled, How to Work with the Microscope, the eye-piece question is only glanced at, and in the last edition of Dr. Carpenter's Microscope and its Revelations, which is universally regarded as the best authority on the practical use of the instrument, we are told that the utility of deep eye-pieces will mainly depend upon the excellence of the objectives, and that the best objectives, by permitting the use of deep eye-pieces, with little loss of light or definition, afford us a clear gain in range of power, if compared with inferior productions that will only work with low eyepieces, through not being able to stand the magnification of their defects.

These remarks are true and valuable; but, like those in the Micrographic Dictionary, they omit the consideration of the advantages which low objectives and deep eye-pieces have, for certain inquiries, over higher objectives and eye-pieces of less power, and it is to this point that I wish to draw the attention of your numerous microscopic readers.

Every one knows that the penetration of low object-glasses