floated instead of being on the ground, that an inconsiderable result was produced.

No. 6, Nov. 28.-The charge, now placed at 30 feet from the

fig. 2. Although only 30 feet horizontally from the ship's side, the effect was so much decreased by the charge being

starboard side, caused great injury to the ship; thwart plates, casks, and fittings suffered severely, and much leaking was caused.

No. 7, May 20.-The charge was placed vertically beneath the starboard side, and the explosion broke the vessel's back, leaving her a complete wreck, as indeed was to be expected.

The general result of these experiments is rather in favour of the ships than of the mines. It is true that the back of an armour-clad ship might be broken rather more easily than that of the comparatively light Oberon; but making all possible allowance, it appears that submarine mines, to effectually close a channel, would have to be so close to each other that an explosion might extend from mine to mine, and the first casualty would open an indefinitely wide gap in the line of defence. In short, the system we proposed to adopt fails, and must be given up. This may be considered a discouraging result to follow on so costly an investigation. It at all events proves the necessity for such experiments, and it is well that they were carried out before the country was involved in more expensive operations. We have now, it may be hoped, time to look for a substitute to a line of large ground mines. We have already mentioned the alternative, namely, a system of small floating charges, which should be fired by contact in close proximity to the ship's side. This change, however, is one involving new difficulties. Tides and currents cause increased complication with this system. Doubtless it may be argued that the action of the small charges, like that of the large ones, depends on the completion of a circuit that may be broken at the will of an operator on shore, so that the channel may be in an instant opened to friendly vessels; nevertheless, the firing will probably have to be effected by gear which is self-acting on the contact of a vessel; and firing at the will of an operator will hardly be attempted. Hence it will be more than ever important to guard lines of submarine mines by powerful batteries, for the process of fishing up charges becomes more easy when the vessel is safe from an operator on shore, and when it is known a charge can only be exploded by actual contact. Moreover, the use of fenders or guards to explode the charges at a distance from the ship's side becomes more feasible.

The next experiments made on submarine defence may be expected to take a new form; 30 to 50 lbs. of cotton is likely to be the maximum charge. The desideratum will be probably a network of such charges floating sufficiently near the surface to catch any vessel at high tide, and yet in place and concealed from view at low tide, with simple galvanic connexions, and not liable to entanglement from currents. This is a problem that may well give Mr. Abel and our officers enough to occupy them for many months to come.

372

THE NATURAL HISTORY OF THE KANGAROO.

BY ST. GEORGE MIVART, F.R.S.

[PLATE CXXVIII.]

THE

HE kangaroos have now become familiar objects to all who visit our Zoological Gardens, or who are familiar with any considerable zoological museum.

Their general external form, when seen in the attitude they habitually assume when grazing (with their front limbs touching the ground), may have recalled to mind, more or less, the appearance presented by some hornless deer. Their chief mode of locomotion (that jumping action necessitated by the great length of the hind limbs) must be familiar to all who have observed them living, and also, very probably, the singular mode in which the young are carried in a pouch of skin in the front of the belly of the mother.

But "What is a kangaroo?" The question will raise in the minds of those who are not naturalists the image of some familiar circumstances like those just referred to. But such image will afford no real answer to the question. To arrive at such an answer it is necessary to estimate correctly in what relation the kangaroo stands to other animals-its place in the scale of animated beings-as also its relations to space and time; that is, its distribution over the earth's surface to-day, in connexion with that of other animals more or less like it, and its relation to the past life of this planet, in connection with similar relations of animals also more or less like it. In other words, to understand what a kangaroo is, we must understand its zoological, geographical, and geological conditions. And my task in this paper is to make these conditions as clear as I can, and so to enable the reader to really answer the question, "What is a kangaroo ?"

But before proceeding to these matters, let us look at our kangaroo a little closer, and learn something of its structure, habits, and history, so as to have some clear conceptions of the kangaroo considered by itself, before considering its relations with the universe (animate and inanimate) about it.