Rifled cannon will in some few years be perfectly constructed of cast steel; the projectile being made of gun metal, i. e., ninety-five parts of copper to five parts of tin, or of lead and its alloys, and at a probable cost of ten times that of a cast-iron projectile of equal weight.
Rifled cannon must be elevated by raising the muzzle; no depression of the breech must occur as by the usual elevating screw; and the recoil must be received and borne by fastenings and axle in rear of the breech only. Trunnions and all impinging influences are incompatible with correctness of fire. The muzzle must be raised in a similar manner to the raising of a hand rifle, the recoil being thrown backwards, in as direct a line as possible with that of the shot.
It is only on account of the difficulty of experimenting with rifled cannon that they are at all behind rifled muskets in point of perfection. The ardent lover of science is appalled when an experiment costs hundreds of pounds. We have not a General Jacob everywhere who can afford to spend a thousand or two in experiments; but, nevertheless, the lover of science, could he experiment, might attain such extraordinary accuracy of range, as to blow up a smaller magazine than that of Kurrachee at four times the distance; and that, too, with a more certain effect, though with a projectile heavier than several of Jacob’s rifles tied together. Correct direction is certain in proportion to the increase of weight; deflection being in the minimum with the heavier weight, from the well known law of momentum. That astute and energetic sovereign, the Emperor Napoleon, is pursuing experiments with rifled cannon; with what result there can be little doubt.
It must be by the use of rifled cannon that our artillery will regain the place it has lost. A short time will suffice to make the disparity between our artillery and small arms as great as when we were content with the six-pounder field gun and old “Brown Bess.” Ranges will only be ruled by sight, and objects will be hit eventually with as much ease at 5,000 yards as they now are at 1,000. Steel, rifled cannon, and projectiles of gun-metal will assuredly bring about as complete a revolution in artillery as the Greenerian rifle and bullet have effected in small arms.
The form of gun best suited for all purposes has yet to be determined; and we have pointed out these defects in our artillery with the hope that some of the great practical philosophers of the present age may devote themselves to the study of this question. It is nearly allied to the science of bell-making, and a few more fractures of Big Ben will extend our knowledge of the subject, and produce a remedy which lies not very deep below the surface. The laws which should guide us in the construction of cast steel guns, so as to insure their durability, are very analogous to those which determine the durability of bells; for the laws which regulate disintegration of crystalline structures are very similar. Hitherto the rule of thumb has, unfortunately, been the only rule observed in measuring out the quantity of metal which shall surround that portion of a cannon which has to sustain the most violent concussion.
Professor Barlow many years ago proved, to the satisfaction of the Institution of Civil Engineers, that the metal in any cylinder decreases in utility in proportion to the square of its distance from the centre: that the outside of a gun of the form now used, in fact, is only one-ninth as useful as the inside; being three times as far from the centre. If we double the thickness, the outside, being five times as far from the centre as the inside, will be but one-twenty-fifth as useful; or in plain English, nearly useless. The reason of this is simple, and I will endeavour to explain it.
“A bar of cast iron one inch thick each way and 40 inches long will stretch about one-twentieth of an inch, if a weight of about four tons be suspended by it. When the weight is removed, the cast iron nearly recovers its previous form, and is uninjured; but if it be stretched more, by a greater weight, it is permanently injured.
“A bar of the same thickness, but three times as long—120 inches—will stretch three times as much, or three-twentieths of an inch, with the same weight; or if only one-third the weight—one ton and a third—be suspended, it will stretch one-twentieth of an inch, the same as the shorter bar.
“If we suspend 16 tons by four bars, one inch thick and 40 inches long, they will each stretch one-twentieth of an inch only, and remain uninjured; but if we attempt to do so with two bars 40 inches long and two 120 inches long, then, when the whole have lengthened one-twentieth of an inch, the short ones are exerting a force of eight tons, but the long ones that of only two and two-thirds tons. The weight, therefore, will still further lengthen the bars, and permanently injure the short ones; perhaps break them first, and then the long ones.
“This is the way a gun is burst. The inside is a series of bars of iron, say 40 inches long, in the form of a ring; the outside a series of rings, representing the bars three times as long.”