tains to beams, viz.: How many successive strains from charges of gunpowder will the former stand before fracture ensues? It is obviously correct that strains often repeated ultimately tend to rupture; and it appears evident that we cannot with impunity continue these forces unless we are prepared to incur the risk of fracture. It is therefore necessary in homogeneous metals-and in cast iron in particular--to ascertain as nearly as possible the law of endurance, and the means requisite to be employed to attain that desideratum. 6. Some attempts were made in this country to cast our heavy ordnance hollow, on the American principle; but the introduction of wrought and homogeneous metal and steel rendered the use of cast iron in the manufacture of guns no longer necessary. We may, however, refer to five experimental cast-iron 24pounder guns, cast at Warrington, under the direction of the author, in 1855. The iron of these guns contrasts rather more favourably with the American metals, although it must be admitted that the American irons have the preference of increased density and increased tenacity over those of this country in the ratio of about 1: 95—or, in other words, the American iron is 15 parts stronger.* The information given in these pages would have been more complete if we could have given in detail the present improved state of rifled ordnance, as manufactured by the different makers and inventors. We have not less than five or six claimants for as many different kinds of guns. They have each their own peculiar mode of construction; and as they are, and have been, almost continually improving and changing their plans and material of manufacture, it would be an endless task to attempt a description of what has been done and is now doing. All that we can do is to give a short outline of the material and its adaptation as applied by the different makers, and leave to abler hands, or to the makers themselves, to work out the construction according to their own individual views and the efficiency of their respective guns. 7. For a series of years past, and up to the time of the Crimean war, when His Majesty the Emperor of the French first introduced the new system of protecting the sides of ships with armour, the * Vide Appendix I. Board of Ordnance and the Admiralty of this country never lost sight of the advantages of having the armament of the Navy of greatly increased power and weight. These advantages were confirmed by the introduction of the 68-pounder cannonades, and the difficulty of penetrating armour-plates led to an entirely new description of gun-construction, which, for these purposes, has to a great extent superseded the 68-pounder. This gun was, however, a powerful and effective weapon, but it was deficient in range and velocity; and to obviate these difficulties, and prepare for an entirely new system of naval warfare, the Government gave every encouragement to inventors for guns of long range and precision of fire. Captain Blakeley, Mr. Whitworth, and Mr. (now Sir William) Armstrong were the first in the field, but only as experimenters -Mr. Whitworth on the small-arms rifle, and Captain Blakeley and Sir William Armstrong on the construction of 10 or 12pounder wrought-iron rifled guns, the latter of which were submitted to the Government, and were highly approved. The result of this was a C.B. and a knighthood, accompanied with the office of ordnance constructor, to Mr. Armstrong. At Elswick and Woolwich an immense number of guns were manufactured, varying from 12 to 600-pounders, under his superintendence. Sir William Armstrong's guns have all, until recently, been constructed on the coil system, which may be described as follows: The barrel is formed of wrought-iron bars wound spirally round a mandril. They are then welded in a furnace erected for the purpose, turned and hooped, until the required thickness and strengths are obtained. The hoops are of different thicknesses, according to position, and they are carefully bored and turned, in order to fit with great exactitude and give the due proportion of resistance to strain. In Sir W. Armstrong's manufacture the hoops are shrunk on to the barrel. Mr. Whitworth, however, adopts a different system, and depends entirely upon the accuracy of his fittings. The homogeneous barrel in this case is made slightly conical, and the hoops are forced on by hydraulic pressure to a uniform state of tension. Large and powerful hoops-one, supporting the trunnions, is fixed near the centre of gravity to balance the gun, and the others, after being carefully bored and turned-are fitted round the breech and the muzzle; it is then built up in the shape of a gun, and being bored, turned, and rifled, is ready for service. This may be taken as a brief description of the Armstrong gun; but, owing to occasional flaws in the welding of the spiral coils, it has been found necessary to adopt Mr. Whitworth's plan, and, in place of the coils, to introduce a perfectly homogeneous barrel of steel, and then hoop with wrought or homogeneous iron, in the way already described. Mr. Whitworth's system has always been to bore the barrel out of the solid, and he adopts this method in every description of gun which he manufactures. He then hoops, as already described, with the same if not greater exactitude, all his heavy guns, and thus attains a uniformity of strain calculated to equalise and increase the resisting powers of the structure. In the smaller description of ordnance the hoops are dispensed with, excepting only for the trunnions, which encircle the barrel near the centre of gravity, as referred to above. Captain Blakeley, Mr. Mackay, and others follow the plan of introducing the solid barrel and the subsequent process of hooping; but a number of Captain Blakeley's guns of wrought iron have been entirely forged and welded by Mr. Clay, at the Mersey Forge, Liverpool, and bored from the solid. It is, however, now found that the homogeneous steel barrel carefully hooped is a preferable and safer instrument for purposes of war than either the cast or the forged wrought-iron gun. Captain Palliser, in order to make use of the present existing guns of cast iron, such as the 68-pounder, has introduced a system of lining the bore with a homogeneous barrel of steel. This not only increases the strength of the gun and removes part of the strain from the cast iron, but it enables him to apply the rifling principle, so as to increase the range and powers of penetration of the gun when fired against iron armourplates. Under all these forms of construction, it becomes a question for consideration whether or not the Bessemer system of manufacture of steel can be applied to the casting hollow guns under hydraulic pressure, so as to give increased density and tenacity to the metal, and entirely to dispense with the system of hooping, which is both expensive and insecure. With a properly-constructed and a well-regulated hydraulic apparatus, much may be done in this way; and by adopting the American system of cooling, affording to the molten mass a free arrangement of the particles for adhesion in its molecular construction, a much stronger and very superior class of ordnance may probably be introduced. It has been stated that castings for guns are greatly improved by keeping the metal in a state of fusion for a number of hours before casting, and in order to equalize the strains arising from unequal contraction-one part cooling before another-it may be desirable to allow time for a more perfect adjustment of the crystals, as exhibited in the American experiments to which we have referred. Supposing that the Bessemer steel, when passing from the fluid to the solid state, follows the same law in its crystalline formation as cast iron, we then arrive at the important conclusion that as much time as possible should be allowed to the process of cooling, in order to obviate the unequal strains of contraction which pervade to a greater or less degree every description of crystalline structure. Independent of the Bessemer system of casting steel into ingots, great advantages would be gained by submitting those intended for the barrels of guns to consolidation under the hammer. This process would in a great degree relieve the mass from the strains of elongation and compression which in every description of casting is present in passing from the fluid to the solid state. In the manufacture of ordnance, whether composed of steel or cast iron, it is desirable that the laws of cooling and crystallization should be carefully observed, in order to equalize the contraction and render the casting as free from strain, and as uniform as possible in its molecular formation. 153 CHAPTER IX. ON THE PROPERTIES OF IRON ARMOUR-PLATES, AND THEIR 1. THE best mode of employing armour-plates for the protection of the sides of ships is a problem yet to be solved, and although we have had several practical examples of their powers of resistance, as exhibited in the ironclads, monitors, &c., of the American navy in actual service, the results are far from satisfactory as regards the question of attack and defence. During experiments of nearly four years' duration, at Shoeburyness, the improvement in the manufacture of guns has outweighed that of the plates; and although plates can be made that will resist shot from the largest guns ever yet constructed, they are, nevertheless, of no practical value in the shape of armour-clad vessels against large guns, as we are limited in weight to the carrying powers of the ship. This being the case, it becomes a question of the deepest importance to devise a description of armour that a ship can carry, and which is at the same time capable of resisting the immensely heavy and powerful ordnance now being constructed. 2. The recent bombardment of Fort Fisher by the Federal ironclads and monitors throws some light on the subject, and the report of Admiral Porter on the question of armour-plated vessels is not without value. It must, however, be borne in mind, that the guns in the fort were, neither for weight nor number, a match for those in the fleet; and having to sustain an attack from vessels that poured in a storm of shot and shell for three successive days, the latter alone amounting to 25,000, it is not surprising that so little damage was inflicted upon the vessels engaged in the bombardment. Admiral Porter in his report states that 'his late experiment with the monitor-class of vessels, under fire at sea and in |