would be inconceivably minute; so that we can scarcely conceive that, above that level, any atmosphere capable of supplying an appreciable amount of light can exist, still less that any atmosphere can extend to the enormous distances at which portions of the corona have been seen to lie above the sun's surface.

It seems to follow, as an inevitable conclusion from this reasoning, that the corona must consist of some sort of matter -discrete solid or liquid bodies, vaporous masses, or groups in which solid or liquid bodies are intermixed with vaporous masses-travelling around the sun. There appears to me absolutely no escape from this conclusion, when we merely consider the evidence against other theories; for I can conceive no other theory of the corona besides this one and those others which we have been forced to reject.

The negative evidence thus bringing us to this particular theory, however, it will be well that we should enquire how far we have positive evidence in its favour.*

In the first place, let me invite attention to what Leverrier has demonstrated respecting the motions of Mercury. The secular motion of the perihelion is not such as it should be if the whole mass of matter within the orbit of Mercury were within the visible boundary of the sun. The conclusion, to which Leverrier has been led by this circumstance, is that a zone or band of small planets exists within the orbit of Mercury. A single considerable planet would produce changes in the motions of Mercury in his orbit, not a change such as is actually observed in the orbit itself. A single planet, then, is not in question, but many. The change, in fact, resembles that produced on the orbit of Mars by the family of asteroidal planets.

Now we cannot neglect such evidence as this, because it is precisely that sort of evidence which has been found most reliable. Unless observation has erred in a systematic and most singular manner, there is a family of small bodies within the orbit of Mercury. What the nature of the family may be Leverrier's researches do not tell us; but, as observations

In a review of my "Other Worlds" in the Quarterly Journal of Science (a review with which I have every reason to feel satisfied, and which has obviously been written by a thoughtful student of science), it is urged that I am too anxious to show that every point of evidence favours a theory of mine-though some points may be urged as well in favour of other theories. I cannot too strongly express my conviction that this anxiety is the very essence of safe theorising. If a theory is clearly opposed by one single point of evidence, it must go overboard, even though a thousand other points seem to favour it.

made during eclipses have revealed no bright points of light,* we may fairly conclude that there are many very small bodies instead of a few bodies of considerable dimensions. Crowds of such small bodies could scarcely fail to be discernible by their combined light during the total obguration of the sun.

Thus, by an independent line of reasoning, it has been shown that light might be looked for where the corona is actually seen. But, again, Mr. Baxendell has been led to infer, from observed meteorological and magnetic changes on the earth, that a zone or ring or disc of matter surrounds the sun, extending to a distance closely corresponding to that assigned by Leverrier to the family of planets. The evidence adduced by Baxendell is of a very striking character, and seems almost inexplicable save on the hypothesis he adopts. And clearly, if such a zone or disc of matter exists, we might expect to see it during total eclipse.

Here, then, is a totally distinct reason for expecting that some such object as the corona would appear when the sun is eclipsed.

Then there is the zodiacal light-demonstrably not a terrestrial phenomenon, since it rises and sets with the celestial bodies as the earth rotates. We see this light during the twilight hours; we recognise a gradual condensation towards its core, and still more markedly towards the place of the concealed sun. Is it reasonable to believe that this condensation is suddenly checked before the sun is reached? Or if we assumed this, must we not yet believe that the zodiacal matter forms at least a zone around the sun? so that, despite the imagined gap between it and the sun, its light would in appearance reach to the sun's place, did the background of dark sky but reach so far.

Here, then, is a new reason for expecting that during totality light would be seen around the sun.

Then, again, there are the meteor systems, of which the earth encounters more than a hundred, all whose perihelia must necessarily lie within the earth's orbit. The chances are so enormous against the earth's encountering one such system, unless many millions existed, that we are forced to conclude that there are many millions for each system actually encountered by the earth. This is, be it remarked, not a hypothesis, but an inevitable conclusion. These meteor systems, illuminated as they must be by the sun, would be visible where the corona is, even if the perihelia lay as far from the sun as the earth's orbit. But passing, as many must, quite close to him, they must be illuminated yet more brilliantly-probably rendered incandescent, or even vaporised, by intense heat.

With perhaps one exception during the American eclipse,

Here, then, is yet another reason for expecting that when the sun is eclipsed light would be seen around him.

The perihelia of comets, again, are known to be very richly distributed in the sun's neighbourhood as compared with more distant regions. Considering that for every discovered comet hundreds escape discovery (a circumstance recognised by all astronomers), and adding to that consideration the discovery that a proportion, at any rate, of known comets have trains of meteoric attendants, we have fresh reason for expecting that the sun's neighbourhood during total obscuration would be a region of brightness.

Lastly, Venus and Mercury, when in inferior conjunction, are seen to be projected as dark bodies on a relatively bright background. The light which illuminates that background would undoubtedly be discernible during the total obscuration of the sun.

Against the theory to which we have thus been led, both by the weight of positive evidence against all other theories, and by the overwhelming weight of evidence in its own favour, no evidence has ever, I believe, been adduced. No one has pretended to point to a single argument which seems opposed to the theory. Nor has any attempt ever been made to support the other theories under the weight of those arguments which have been urged as conclusive against them.

Thus, then, the matter rests at present. I would submit to those who desire to see the cause of astronomy successfully advanced, that a case has been made out for directing future observations to the analysis of the structure and physical condition of a veritable solar appendage, in place of wasting the energy of observers in the attempt to resolve a question which has already been fully answered. If, next December, observers regard the corona as a solar appendage, numberless ways of determining what the nature of that appendage may be can scarcely fail to suggest themselves. Observations made with such an object, and according to methods so suggested, cannot fail to be most instructive and useful. But if, on the other hand, observers regard the corona as an object whose real position in the solar system is undetermined, as an object which may be ninety millions of miles away round the sun, or a quarter of a million of miles away round the moon, or close by within a few hundred miles of us in our own atmosphere, it must needs be that their observations will be ill-directed and relatively valueless. This consideration, and only this, has led me to dwell as strongly as possible, while there is yet time, on considerations which (as I take it) are amply sufficient to guide the thoughtful student of nature to a just general opinion as to the position of the corona in the solar system.

391

MACHINE-GUNS, OR MITRAILLEUSES.

By S. J. MACKIE, C.E.

FOR

OR some time past the public have heard of experiments with machine-guns at the famous government shootinggrounds at Shoeburyness, and the reports of these trials, and the notoriety weapons of this nature have attained in the fearful battles which have recently been waged on the Continent, have combined to give the keenest interest to this subject. The French went into war with much boasting over these terrible mitrailleuses, and these new arms, it is clear, must have made their mark, or we should not now hear of their contemplated introduction into the Prussian armies. The Prussians, like ourselves, have preferred artillery; and, without doubt, if the sole option of one or the other were a necessity, and judgment lay between rifled field-guns and mitrailleuses, the choice of the former for general service would be right and proper. The field-gun can fire buildings, destroy material, and make a breach; whilst the mitraille contained in its shells is carried to long distances with the force of a large charge of gunpowder. Nevertheless, the machine-guns throwing compact clouds of bullets, or streaking with thin horizontal lines. the front of the enemy, have special deadly uses, and are, indeed, for certain purposes, most terribly destructive weapons. The war has already done this good-that it has, at least partially, awakened this country to a sense of its military, if not national, insecurity; and the popularisation of some of the prominent items of military mechanical and physical science will serve a very useful purpose at this time, in respect to the discussions which have so freely been awakened.

Of the French mitrailleuses no specimen has yet been brought to trial in this country; but two weapons of the class of machine-guns have undergone an extensive, though not as yet by any means an exhaustive, test. These two are the Montigny-Christophe mitrailleuse and the Gatling machinegun. The former (fig. 1, Plate 66) is a composite weapon,

containing numerous-the one under trial thirty-seven-ordiLary rifle barrels, with hexagonal exteriors, packed together and soldered into a wrought-iron jacket or cylinder; it is discharged by a descending plate, which allows the separate springs in thirty-seven corresponding chambers to thrust forward their respective pistons to fire the cartridges in front of them. The cartridges are of the class known as "central fire,” and very similar to those commonly used in the British service for the Snider rifles of the infantry.

The gun, for the sake of explanation, may be regarded as in three parts: (1) the cylinder of thirty-seven barrels; (2) the breech attachments or breech-box, consisting mainly of two deep vertical side-plates, between which the (3) breech-block slides horizontally to and fro, supported on suitable projections. The breech-box is screwed on to the cylinder of barrels by a ring, and has its rear end closed in by a transverse bar or plate. The breech-block contains the arrangements for firing the cartridges, and when pushed home by the lever closes the whole of the barrels at the rear. In the metal of this breechblock are bored short chambers, corresponding in number and position with the barrels; in each of these is a small steel flanged piston pressed upon by a spiral spring. A plate perforated for the protrusion of the striking points of the pistons covers the inner face of the block. In a space in front of this face the steel plate or shutter slides vertically up and down. In front of this, again, is an outer face-plate, containing as many small steel strikers as there are barrels-in this case, thirty-seven. When the lever is pressed down, the breechblock is forced forwards and closes the gun, and the springs acting on the pistons are put in compression, the pistons then pressing against the vertical sliding-plate or shutter. When the handle of the wheel-gear moving the shutter is worked, the edge of the shutter descends, and as it clears each piston in succession, the latter dart across the vacant space and drive forward the strikers upon the fulminate in the cartridges. The edge of this shutter is bevelled, to ease the action of striking, and is also serrated, or cut into steps, in such a way that no two contiguous cartridges can be fired, the distending effect of the gases diverting the shots when the proximity is too close. When the breech-block is drawn back, a thick steel plate, perforated with thirty-seven holes, into each of which a cartridge is placed, being prevented from falling through by a tight fit and by the flange intended for extraction, is inserted in the opening. When the breech-block is slid forward again the cartridges are pushed into the open rear ends or chambers of the barrels, and the gun is closed up ready for firing. These ammunition plates are replaced as fast