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force; whereas the smooth-bore delivers only spherical projectiles unaccompanied with any sensible amount of friction. The initial velocity of the shot of the rifled gun fired with the usual and smaller charges of powder is about 1200 feet per second, while that of the smooth-bore is about 1600 feet per second; but the velocity of the former decreases in a much inferior ratio to that of the latter, which is accordingly speedily distanced by the rifled shot. Moreover, the line of flight, or, as it is technically termed, the trajectory, of a rifled gun is much less curved than that of a smooth-bore, and this is a point of importance, inasmuch as the efficiency of a shot depends greatly upon the directness of its course. The initial velocity of the rifled shot with its smaller proportionate charge of powder being, as we have said, less than that of the spherical shot, it has been assumed that even with equal charges the round shot would have the advantage in velocity owing to the facility of its exit from the smooth-bore barrel. The superior vis viva of the round shot is still frequently urged. This assumption is, however, erroneous. Fired with charges in the same proportion relatively to the shot, the rifled gun projects its shot with at least equal initial velocity, as conclusively demonstrated by experiments at Woolwich and Shoeburyness. While in the smoothbore there is considerable windage, or in other words, much gas escapes round the loose-fitting shot; in the rifled gun the windage is in a greater or less degree suppressed, and pro tanto the force of the powder is more completely utilized. Hence it appears that rifled artillery has not only vastly the advantage over smooth-bores at long ranges, but that even at close quarters it may be easily rendered equally effective. It is extremely important that the mistaken notions which prevail in the public mind on this subject should be corrected-notions which have been sedulously propagated by those whose experience has been restricted to smooth-bores.
Every civilized nation has adopted rifled ordnance for the field, but none has as yet committed itself exclusively to rifled heavy guns. This fact would furnish a formidable argument against the superiority claimed for heavy rifled ordnance, were it not reasonable to suppose that it may have arisen from want of ability to construct large rifled guns of sufficient strength and endurance. The great question in heavy rifled ordnance is how to produce guns possessing these essential qualities, and to this the particular method of rifling and of loading is altogether subordinate. We ought, therefore, in the first place to consider the various modes of construction which have been of late proposed with a view to the solution of this great problem.
We may remind our readers that the most ancient guns were made exclusively of wrought-iron, on what is termed the built-up' system. They were composed of longitudinal bars fitted together and firmly braced with external rings or hoops of iron. In those days wrought-iron could not have been employed in any other manner, as machinery suitable for large forgings did not then exist. The most familiar example of a gun of this description is the famous Mons Meg, now at Edinburgh. The legendary history of this gun is curious. It is said to have been made by a blacksmith called McKin, out of bars of iron contributed by the people of Kirkcudbright, during the siege by James II., in 1455, of Threave Castle, the last stronghold of the Douglas family. Mr. Mallet, quoting 'The Statistical Account of Scotland,' informs us that its weight was 6 tons, and its calibre 19 inches; the charge of powder was a peck; and in a short time the garrison surrendered.' We are further told that the name 'Meg' was derived from McKin's wife, whose voice was said to rival that of her namesake.' Mons Meg was a gun of a calibre far exceeding any known in our own day. So also the Kemerlicks of the Dardanelles reached the enormous calibre of 28 inches. These ancient guns were, in fact, specially designed of this great capacity in order that they might carry rough masses of stone, slowly projected by inefficient charges of feeble powder. No sooner was the quality of the powder improved, and the use of cast-iron shot established, than these wrought-iron guns were found no longer safe; and by the end of the fifteenth century, according to Mr. Mallet, they fell wholly into disuse.
Next in order came cast guns, composed of the alloy of copper and tin called gun-metal-a variety of bronze now commonly but erroneously designated brass. Bronze guns speedily became general. The reduction in the calibre and size of guns increased the facilities for using that metal, the casting of which dates from remote antiquity. Its toughness and tenacity rendered it in every way suitable for the requirements of that day; and, indeed, at the present time the field artillery of Europe is for the most part composed of this alloy. It was used in the construction of the largest guns; for the cost of wrought iron, and the difficulty of its manufacture, were then much greater than at present. The history of cast-iron ordnance is involved in some obscurity, but the first English guns of this material are stated to have been founded in Sussex, in the sixteenth century. It is, however, doubtful whether the art was not
*On the Construction of Artillery.' belief in Scotland is, that the gun came from † Lower's Contributions to Literature.'
London, 1856, p. 183. The current
imported from the Continent. The cast-iron of early times, smelted with charcoal, was far more suitable for artillery than much of the cast-iron now smelted with coke. There is no metal which is subject to greater variation, both in its chemical composition and its mechanical properties, than cast-iron. As an illustration of this fact we may refer to the mortars captured at Bomarsund, the iron of which was smelted by the Russians with charcoal, and to our own mortars which so strikingly failed at Sweaborg. Under all circumstances cast-iron is essentially a brittle material; and it is hardly conceivable that any persons practically acquainted with its properties and those of wrought-iron would recommend it as a material for cannon, if they could construct solid and durable guns of the latter metal, and were able to bear the additional expense therein involved. We remember to have seen a cast-iron high-pressure steam-boiler, but who now would dream of such an application of that untrustworthy metal, which Captain Jerningham, in his evidence before the Committee on Ordnance, has so naïvely compared to crockery? Guns of castiron burst without warning, scattering huge angular fragments of metal far and wide; whereas guns of wrought-iron generally give timely notice of their approaching failure, and, when they do burst, are comparatively harmless. However carefully the foundflaws in the interior will occasionally exist, which we have no means of detecting; whilst in a wrought-iron gun, built up piecemeal, we can be sure of the soundness of the metal at every step. We do not pretend that cast-iron guns have not rendered most efficient service, and given evidence of great powers of endurance, but we do maintain that there is no comparison between these varieties of iron with respect to their suitableness for artillery, especially in the case of rifled cannon, which, as we have stated, are subjected to a much greater strain than smooth-bores.
ing of cast-iron may be conducted o
But this conclusion in favour of wrought-iron guns rests upon the assumption that they can be manufactured with the requisite soundness and solidity. Such guns have been manufactured on two principles, viz., by forging in one piece, and by building up in several pieces. The most effective forged guns have been made at the Mersey Steel Company's Works, under the able superintendence of Mr. W. Clay, than whom no one has attained greater skill in the art. Such guns may be constructed out of either a solid or out of a hollow forging. The 'Horsfall gun' was made on the first system, and the Prince Alfred gun' on the other; but, notwithstanding our present facilities for working huge masses of iron under the hammer, great difficulties have to be encountered.
The metal must be repeatedly exposed to a high temperature, a condition favourable to the development of a largely crystalline structure in the interior; and it may be shown that such a structure is injurious to the tenacity of the metal, for, cæteris paribus, in proportion to the size of the surfaces of the crystals will be the facility of fracture. Although hammering may tend in great measure to counteract this defect by disturbing the action of the crystalline forces, yet in the case of large masses the interior must remain for a much longer time at a much higher temperature than the exterior, and, when the latter has cooled down to a certain degree, it would be rendered more or less hard and brittle by continued hammering. This it is which constitutes the essential and inherent difficulty in manipulating large thick masses of iron under the hammer. Moreover, it is impossible to ensure absolute soundness of weld in every part. In hollow forgings there will be probably less difficulty from these causes, for the obvious reasons that there will not be the same difference in temperature in different parts of the mass; that the interposed cinder, which wherever it occurs will occasion unsoundness of weld, may be more perfectly extruded; and that the blows of the hammer will operate more uniformly throughout.
Of late we have heard much of the applicability of steel to artillery. This metal, being fusible at temperatures attainable in our furnaces, may be founded like cast-iron, and accordingly guns of cast-steel have recently been produced, especially by Krupp, of Essen. Steel, in a chemical point of view, approximates to cast-iron, and has been actually classified as such by Karsten, the great German metallurgist. But steel castings, in order to acquire the necessary degree of tenacity, must in every case be subjected to the process of hammering; and then in large castings the same difficulties arise, though in a less degree, as in the case of wrought-iron, with the exception that there is no cinder to be expelled. As steel, after hammering, is greatly superior in tenacity to wrought-iron, it has been recommended as especially adapted for ordnance. It should, however, be borne in mind that tenacity-that is, the power of resisting rupture—is always determined experimentally by the gradual application of the rupturing force. It by no means follows that the tenacity of steel will be the same when the rupturing force is suddenly applied, as in the case of the explosion of gunpowder. This is a point which can only be satisfactorily determined by experiments upon steel guns themselves. The casting of steel in large blocks, free from cavities, is attended with great difficulty, which as yet few, if any manufacturers, have been able successfully and uniformly to overcome, and, as in the case of cast-iron, we have
no means of discovering internal flaws. If cavities exist, they may
It will be observed that the preceding remarks with regard to cast-iron, wrought-iron, and steel, are intended to apply only to guns entirely composed of one or other of these materials used in mass. We have yet to consider what results have been attained by the employment of the same materials when built up piecemeal, and used in combination in the construction of ordnance. In order to meet the increased requirements of rifled artillery, it has been attempted to employ wrought-iron in combination with cast-iron; that is to say, to strengthen cast-iron barrels with rings of wrought-iron. This plan recommends itself by the facility with which it may be effected, and as affording a ready and cheap means of utilizing existing cast-iron ordnance. The French, the Spanish, and the American Governments, have all adopted the plan. It has also been extensively tried in this country. From the Report of the Committee on Ordnance we learn, that late in 1859 the War Department, at the request of the Admiralty, ordered not fewer than three hundred cast-iron guns to be thus strengthened, and that they were induced to take this step from the receipt of confidential information that the French were engaged in arming their ships with similar guns. It was soon found that no advantage was to be gained by this plan. The comparative experiments with hooped and unhooped guns showed that in some instances the