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 6, 1860.] threshold of progress, we may assume, that whatever man has done, man may yet do a great deal more. Until we have tried with our own guns the ribs of La Gloire, and with our own craft her locomotive qualities, we must not take for granted all that the imaginations of Imperial editors may assert. We remember that La Gloire was once highly spoken of as a steam-ram, and her ram-like qualities were to have been tested on the old Suffrein line-of-battle ship, but the experiment never came off.

The first question in a sea-vessel is stability on the water, as a security against “capsizing,” a word derived from the act of turning head over heels. Ten-gun brigs were formerly remarkable for their facility in this kind of sea-gymnastic, and there was once a Greek fleet built in England wherein the planners were so taken up with the one idea of diminishing resistance by decreasing the breadth of beam, that none of the craft would stand upright either under sail or steam.

The principle of stability consists in keeping the centre of gravity within the base, and so long as this is done we can build a column like the London Monument or the St. Rollox chimney, though the centre of gravity is very elevated. But if an earthquake were to take place, down would topple the columns by reason of the elevated centre of gravity overtopping the base. Therefore the lower the centre of gravity the more secure would be the column. If instead of the column we make a pyramid, we get a form which it is almost impossible to overthrow by any earthquake.

If now we form a body, with the water for a base, the movement of the water represents the earthquake, and the body will be stable, or incapable of turning over head and heels, in proportion as the base exceeds the height and the low level of the centre of gravity. Thus a flat thin board thrown into the water will always float on its flat side, the centre of gravity being in the centre of the mass, and at a very low elevation. But if a sufficiently heavy piece of metal be placed at one edge of the board, it may be made to float with the opposite edge upwards, like a fish.

Again, if we throw a solid cube foot of floatable timber into water, it will float with one corner upwards and the opposite corner downwards, the particular corner being determined by the density of one part of the material over the rest. If the cubic foot of timber be cut diagonally into two equal parts, each of them will float nearly equally well on the broad diagonal surface, or on the two rectangular surfaces. If a long cylinder of wood be placed in the water, the centre of gravity being in the central axis, it will float any side upwards. If a long squared log be placed in the water it will float on any one of the four sides equally well, unless the centre of gravity be nearer one than the other, in which case the heavy side will tend to be the base, and the log will turn to that side if the water be agitated. If the log be cut in two, diagonally, through the whole length, and weight be added at the apex of the rectangle, it may float on its broad base; but every disturbance of the water would tend to roll it over, and it would then take the position of greatest stability indicated by the diagram Fig. 1, which is intended to represent the mid-ship section of a sharp vessel, a a being the water level, and b b the surfaces pressing on the water; c c the deck, and d d the top sides, or bulwarks, above the deck, e the ballast, or weight, tending to keep the apex f in a vertical line, and restore the vessel to equilibrium after disturbance. For a sailing vessel this is the best sectional form to preserve a straight line in the water and prevent lee-way. It is, in fact, almost all keel. But there are many reasons why vessels are not constructed so. First, with ordinary timber framing it is not a strong form to resist the pressure of the water; and, secondly, the sharp vessel will not carry so bulky or so heavy a cargo. The circular form, shown by the dotted lines g g, gives the strongest form to the vessel with a larger carrying power, but with the defect of rolling easily on the water like a cask; and the dotted lines h h show the form of largest capacity in volume and weight, but comparatively a weak form to resist the pressure of the water. For sailing on a wind, the lines b b are the best, the lines h h the worst. For a vessel moved by internal power the form is immaterial, provided the stem and stern be sufficiently acute, and therefore while the mid-ship section is denoted by the lines h h, the stem and stern taper off in the form of the dotted lines i i, and the sharper the taper, the less will be the resistance.

A ship, unless of fir-timber, does not float by reason of the lightness of the material of which it is built, as a raft does, but by reason of what is called its displacement, i. e., in other words, the cubic contents of internal air space, and if compatible with other considerations, the more air space it contains the better, wherefore the lines h h would be the best, being double the lines of b b, and this brings us to the consideration, supposing air space, or, in other words, carrying power, to be sufficient, what is then the best form of hull, and more especially a hull intended to avoid the effect of cannon-shot by a sheathing of armour plates?

A shot produces its destructive effect either by its great weight or force of propulsion, or both combined. If the shot be light, the effects must come from force of propulsion. In any case great range is important. In throwing a shell, the chief effect of which is by the explosion of internal powder, the elevation at which it is fired is of little importance; but in battering ships, or breaching forts, shells are used to strike point blank as well as solid shot.

The armour used for covering vessels, consists of plates of iron or steel in as large sizes as possible. Probably soft steel is the best, being most homogeneous. These plates are bolted to the sides of wooden or iron vessels; the greatest thickness as yet conveniently attained in manufacture being about 4½ inches. In the experiments which have been made, Whitworth rifle shots have punched holes in these plates at 400 yards, and 68-pound shot, not rifled, have shaken the whole fabric of plates and the wooden framework behind it. Whether the rifled shot is essential to penetration is not yet made certain by the “crucial instance” of a plain shot fired from an equivalent smooth bore with an equal windage and equal charge of powder.