certain destruction of the gun-carriages; but as far as relates to offensive means, they may be made greater from a well-constructed square stern, than from a circular one, as we have particularly noted in the case of the frigate Guerriere in our navy, and the others built upon her model. The danger arising from pitching, may not only be lessened by a proper form of the extremities, but by a just distribution of the weight; taking care to load those parts as little as possible. Hence, poops, sterns with a great rake and loaded with carving, quarter galleries, and heavy figure heads, are objectionable, and are now in deserved disrepute. And hence, in time of peace, or on a voyage to a station, a ship may be much relieved by stowing near the middle of the vessel a couple of guns from each extremity of her several decks.

If the action of rolling produce less direct effect in straining a ship, it is still attended with danger, and will also tend to diminish the strength and duration of a ship, through the action of the masts as powerful levers. These dangers arise from the shipping of seas, even on the weather side; and the strain on the masts and rigging by their violent return towards the wind; by the last of which, the sails are frequently torn, and spars carried away. A ship may thus be compelled to return to port to refit, or may be driven upon a lee shore, for want of the power of spreading sail enough to beat off the shore. The greater the stability of a vessel, the more violent and rapid is the motion of rolling, and hence in ships of war, the motion may be relieved by raising the centre of gravity of the weight, or even by adding weight to the upper works. Our author cites the case of two Spanish men of war, the San Carlos, and San Fernando, which were intended for third rates, carrying eighty guns upon two decks, and which never left the harbour without being dismasted. These vessels were rendered serviceable, by mounting heavy guns upon their gangways, thus making them equal in force to second rates. The velocity with which a vessel rolls, may also be lessened, without changing the position of the centre of gravity, and thereby lessening the stability, by merely removing the weight to the greatest possible distance on each side of the plane of the keel. Thus a vessel will roll less violently with her guns run out, than when they are housed. We may also see from this, the error so long persisted in, in naval architecture, of making the sides of ships of the line tumble in suddenly; as in this way, without any augmentation of stability, they will roll more violently. This defect has been slowly and timidly lessened, but we know of no vessel of this class, entirely devoid of it, except the Ohio seventy-four. This rule is not applicable to small vessels.

* Other recently built ships in our navy, have probably the same quality; but we have not seen them.

The best possible figure to give a vessel, in order to moderate the action of rolling and pitching, is that in which every vertical section is a circle, whose centre is the point of application of the forces that cause the inclination. Such a figure cannot be attained in the cross sections of vessels navigated by sails, as the Centre Velique lies too high; but it may be approached, by taking care that the extreme breadth of every section shall be considerably above the water's edge. When, however, no other force acts, except that of the waves, the figure is practicable; and we have familiar instances of its application, in a portion of the rind of a cocoa nut, or of the skin of an orange, that will float in an upright position, upon surfaces the most violently agitated. The same principle has been applied in the construction of the English life-boat, which, by the aid of great buoyancy, (arising from the mass, even when loaded with the greatest quantity of water that can be shipped, being still less in weight than an equal bulk of the fluid,) is capable of navigating the most tempestuous seas.

In addition to the occasional, but frequent straining to which vessels are liable in the action of pitching and rolling, there is a constant one to which they are exposed from the moment of their launching. Although a body plunged in a fluid will speedily assume a position of equilibrium under the joint action of its own. weight, and the upward pressure of the fluid, it does not follow that the vertical action of the fluid is the same at every point, or that it exactly balances the weight which acts there. So far from this, the load of ships towards their extremities is not sensibly different from that in the middle, while a much greater volume is immersed in the latter part than in the former. At the two extremities then, the weight will exceed the upward force of the fluid, while at the greatest breadth, the last of these powers will preponderate. The mode of action of these forces may be investigated, by supposing a vessel to be divided into two equal parts, by a vertical plane at right angles to the plane of the keel. The supporting force will here, as before, be applied to the centre of magnitude of the immersed part of each of these segments, the weight to their centre of gravity. But these two points will not now be in the same vertical line; the line of direction of the centre of gravity falling further from the dividing plane than that of the centre of the part immersed. These equal forces (the weight, and the hydrostatic pressure) will then each act, as it were, upon a lever whose fulcrum is in the dividing plane, and the weight will in consequence have a mechanical advantage over the pressure. The effect of this will be to change the figure of the vessel, by the elevation of the middle, and the depression of the extremities. Such a change of figure is found to take place in all large vessels at the instant of launching. In some ships of the line, it has been found to amount to nearly a foot, in almost all, to

seven or eight inches. The force which thus bends a vessel at the moment of launching, continues to act during the whole duration of its service. It is resisted by the cohesion and strength of the materials, and particularly by the planks, (called the Bends,) that lie between the water's edge and the lower deck ports. As the strength of these planks diminishes with age, the change of figure will increase; and as, from their position, between wind and water, they are more liable to decay than those that are either constantly immersed, or constantly dry, it has not unfrequently happened, that ships, in other respects perfectly sound, have been rendered unseaworthy, or even destroyed by their failure. Hence, in the usual construction, these planks are among the most important parts of a ship, and require to be more frequently renewed than others. And, although they are all above light water mark, they cannot, in large vessels, be safely removed and replaced while they remain afloat. Dry docks are, therefore, on this account, as well as many others, indispensable for the repairs of a navy. The inner, or ceiling planks, also perform their part in resisting this tendency to a change of figure. Both the outer and ceiling plank, however, act to a disadvantage in resisting this action. Its direction is perpendicular to their length, in which way their own elasticity will permit them to yield to it, to a very considerable extent. They are also at right angles, or nearly so, to the timbers that form the frame of the vessel; and it is well known that all such framing is liable to a change of figure. Thus, for instance, a common gate, or a battened door, will speedily fall to pieces by its own weight, unless supported by diagonal braces, and in paneled doors the same consequence is avoided, by filling the vacuities of the framing by inflexible pieces. Obvious, however, as is this defect, it has, notwithstanding, existed uncorrected from the earliest date of marine architecture to our own era. It is only within a few years that the defect has been pointed out, and an appropriate remedy introduced. Seppings, a distinguished British naval architect, has proposed the suppression of the ceiling plank, and the introduction, in lieu of it, of a system of diagonal trusses. In the few ships that have been built upon this principle, the effect has, in a great measure, answered his expectation, although some practical difficulties are said still to exist. The change of figure, at the time of launching, has in them been reduced to one third of what occurs in similar ships of the old construction. We would venture to inquire whether it would not be possible to give to the ceiling plank itself a diagonal position. This, if practicable, would be attended with a still greater increase of strength.

The intensity of the force that tends thus to bend, and finally to destroy a vessel, increases in the compound ratio of its weight and length, or as the fourth power of the lineal dimensions.

Hence, the timbers and planks of vessels ought to increase in size, more rapidly than the tonnage, a rule that is rarely attended to in practice, and which is, in truth, liable to difficulties that seem to mark a limit to the magnitude of ships. Of this difficulty we have an instance in a vessel on which the skill of French naval architects and ship builders was lavished, the Commerce de Marseilles, the largest ship ever launched in France. This vessel, which fell into the hands of the English during their occupation of Toulon, in 1794, was safely navigated to England, with a prize crew, and without the usual stores. But, when equipped to bear an admiral's flag, and loaded with the customary stores, water, and provisions, for the larger crew, the strength of the materials gave away under their weight, and the ship became unserviceable, in the first gale of wind that was experienced. During the Revolution, and the reign of the Emperor Napoleon, the French seem to have restricted themselves to vessels of two decks, and the flag of Villeneuve was borne at Trafalgar by a vessel of that description. But, the Spaniards were successful in building a vessel of even larger size, the Santissima Trinidada; this is, in a great measure, to be attributed to the scientific investigations of Juan. The English, who avail themselves of the discoveries of other nations, have four vessels in their navy little inferior in size to the Commerce de Marseilles, none of which however have a high reputation.

The motion of ships is for the most part affected by the action of the wind. Steam has however been partially introduced, even in vessels navigating the ocean; and it is even confidently anticipated, that it may be made to bear a prominent part. in future maritime wars. Still, however, except upon rivers and small lakes, it is so much more expensive an agent, that it will never wholly supersede the wind as a moving power.

The wind is made to act, to propel the hull of a vessel through the water, by spreading upon masts, in such a way as to intercept a portion of its current, sails of canvass, or other light substance. The exact mechanical action of the wind upon the sails of a vessel, is not fully understood; even the theory of the action of non-elastic fluids, is not entirely developed, and that of elastic fluids, is still less improved. It is, however, generally admitted, that were the sail a plane surface, the direction of the motion it would derive from the impulse of the wind, would be in a line perpendicular to its own surface. The intensity of the force would vary with the inclination of the sail to the course of the wind, but the direction would remain constant. This is sufficiently near the truth for our present purpose. A vessel then, of a circular shape, and consequently equally resisted by the water in all directions, would move forward in a line perpendicular to the surface of the sail. But such a vessel is never used in practice,

nor indeed would it have been possible to steer or guide it; for it would have readily moved around its vertical axis, until the sail had attained a position perpendicular to the wind, and could therefore have sailed in no other direction than directly before it. To obtain the property of sailing, at any angle with the wind, that will permit the sails to fill, vessels have been made with sections more near to an ellipse, than to a circle; and by this change of form, other advantages have been attained. It is desirable that a vessel should sail as nearly as possible in the direction of her length, or in the plane of her keel. The greater the length of the vessel, the breadth remaining constant, the less will be the deviation from this plane. This will at once appear, from a consideration of the nature of the resistance that opposes the motion through the fluid. When a vessel is at rest, the fluid pressing equally upon equal surfaces, is in equilibrio around the hull; but when motion begins, this equilibrium is at once disturbed. The viscidity of the fluid, in the first place, opposes a resistance analogous to friction, which follows the law of the space described, and therefore of the velocity simply, provided both ends of the vessel be nearly similar; the second part of the resistance, and which, in most treatises on the subject, is the only one taken into account, follows the law of the square of the velocity; finally, a wave is raised in front of the vessel, and the resistance arising from this, increases with the fourth power of the velocity. In water, the constant coefficient of the first of these, is much the greatest; so that, in small velocities, the first of these terms alone, need be taken into account; but, as the velocity increases, the values of the other two increasing in a much higher ratio, become sensible, and finally, of such an amount, as to show that no application of mechanical agents can be made to propel a vessel through the water, beyond some finite velocity. Frigates of the best construction for sailing, when struck with a squall, with all sails set, have been observed to move, until the sea rose, with a speed of about fifteen miles an hour; and a steam-boat at present navigating the Hudson, moves through the water at the rate of thirteen miles; we cannot but conceive, that the former of these is probably the utmost limit of speed that any vessel can attain. The exact limit may however be calculated by the formulæ of Juan, but it would not be suited to the objects of our review, to enter into this investigation. Each of these several terms, of which the resistance is made up, depends also upon the figure of the surface of the vessel, or the angle its several parts make with the course. The maximum resistance to lateral motion, would be measured by the application of the formula to a plane surface, bounded by the cutwater, the stern-post, the keel, and the surface of the water; the maximum resistance to the direct course, by the application of the same formula to the greatest cross sec