Part 50 (1/2)
If you suppose a bar, say an axle of uniform section and uniform quality in every respect, it will bear bending into extraordinary forms even by a blow; and if you a.s.sume that portions of it become more tenacious and stronger, but remain equally elastic, the ultimate strength of this bar will not, I think, be materially increased or diminished; but if you suppose the elasticity of these portions either increased or diminished, I believe the ultimate strength of the bar under a blow is diminished. In like manner, I imagine that in the section of a gun barrel, if portions are more or less elastic than others, or at all different in their character, not only many points of fracture may be determined on, but that the whole may be rendered much less able to resist the violent explosion. The strain produced by the explosion and the plane of fracture is almost certain to be in a plane pa.s.sing through the longitudinal axis, and therefore I had a.s.sumed that one would avoid as much as possible having any variation of quality which f.a.gotting must produce to some extent in planes in this direction. To attain this end, I had endeavoured to scheme some way of welding up 'cheeses' or discs, which might be hammered up splendidly h.o.m.ogeneous of the full diameter and of a considerable thickness, and I wish that you would scheme the best way of welding them together. I should suppose that the centre surface might be welded, and wedges welded in all round, or some other mode devised, bearing in mind that the strain in any plane transverse to the axis is small, only that arising from the recoil of the breech and the friction of the shot.
I have also an impression that something harder than ordinary wrought iron is wanted for the inner surface to resist the explosion. This you might give probably in f.a.gotting up. I am trying the effect--as much for the amus.e.m.e.nt of the thing as with any great expectation--of a cylinder of hardish material wrapped round with iron wire, laid on with a certain amount of tension proportioned to the diameter. Such a barrel ought to be strong--whether practically successful is another thing.
The scheme of making a gun with the barrel wrapped round with wire, which is referred to in this letter, was one which Mr. Brunel and Mr.
Armstrong were very desirous of making the subject of actual experiment.
Whether or not it would under their hands have become practically successful, could not be ascertained, as they were obliged to abandon the project, in consequence of the wire covering being patented, in May 1855, by Mr. Longridge.
The following letter to Mr. Armstrong relates to the same subject, and is interesting not only as showing Mr. Brunel's correct appreciation of a principle which is the essence of the coil system of constructing guns, but as further ill.u.s.trating his objections to the patent laws:--
June 8, 1855.
Have you ever done anything towards my experiment of the wire gun?
I have been anxious for some time past to learn about it, but have waited to see you; to-day I learn that Longridge is taking out a patent for it. I daresay it is his own idea, and I only regret it, as I suppose it will now prevent my pursuing it; and I think it likely that with your a.s.sistance we should have succeeded in making at least as good a gun as he will. The principle I am disposed to think good; the success would depend upon the practical application, and but for these patents, the more compet.i.tors the better for the public. As it is, compet.i.tion is destroyed. Let me know if you had done anything. Pray let me know also what you are doing about your own, in which I feel equally interested.
Mr. Brunel had also considered the advantages of making the bore of the gun polygonal, with a projectile shaped to fit it. He had a portion of cannon tube and a projectile made by Mr. Armstrong in the beginning of 1855, but he did not himself pursue the question further.
Indeed, after the middle of the year 1856, when the works of the 'Great Eastern' steam-s.h.i.+p began to occupy a large portion of his time, Mr.
Brunel was unable any longer to take part in gunnery investigations; but he watched with unabated interest the proceedings of those friends who have continued their experiments, with the great practical success of which he lived to see only the beginning.
_Floating Gun-Carriage._
The plan of a gun-boat, or, as it would be more correctly called, a floating gun-carriage, which Mr. Brunel designed for an attack on Cronstadt and other Baltic forts during the Russian war, is clearly described in the following memorandum, which he drew up for the information of the Admiralty:--
December 20, 1855.
The principle is simply the fixing a very heavy gun in a floating shot-proof chamber or casemate, exposing the smallest possible surface; that surface to be of such a form as to be struck by shot only at a very oblique angle; and the gun being a fixture, with the means only of elevating and depressing to an extent of 10 or 12 degrees, but with no lateral motion, the port or embrasure need be only of the size of the muzzle of the gun, so that the gun, the men working the gun, and everything on board will be perfectly protected.
The gun will be directed by elevating the breech, and by slewing the vessel slightly and slowly backwards and forwards across the line of aim, by means afterwards explained.
The men loading the gun will simply load as quickly as they can, and when the gun is loaded push out a trigger.
The governor or person directing the gun will stand behind the hood or chamber, looking direct at the object through a telescope of low power, fixed horizontally in the axis of the vessel, and made to move vertically parallel with the axis of the gun, and mounted with reflectors; so that both telescope and man are completely under cover, and he, keeping the vessel truly in range and the elevation correct, will only touch the trigger whenever his line of sight crosses the object.
The vessel will carry a small engine, of power sufficient to drive it for a short time at a good speed, say eight or nine knots, and at other times to keep up a small forward motion to counteract the recoil, and to keep the vessel's head moving a few degrees right and left across the line of range.
A sufficient portion of the vessel to contain and to float the gun, ammunition, and engine, will be shot-proof.
A fore-body and after-body, the top of which will be _a fleur-d'eau_, or a few inches under water, will be added, to give such a form of entrance and run as will admit of the vessel attaining the speed mentioned; but these parts will be mere sh.e.l.ls, and may be full of water, and if damaged by shot will not affect the buoyancy of the float, besides which, not being above the surface of the water, they cannot be much exposed to injury.
The mode of propelling may be by a screw, but I prefer the 'jet,'
which, whether an economical mode of propelling or not, is a sufficiently good one for this purpose, and exposes _nothing_ whatever to be injured by shot.[185]
Whether propelled by jet or not, I should have two small lateral jets for directing the vessel, such jets being governed by two c.o.c.ks handled by the gunner.
Such a mode of directing the aim by a man under cover looking through a telescope, with one hand directing the gun and the other on the trigger, will admit of an almost unlimited degree of accuracy.
The gun being in a perfectly shot-proof casemate, machinery may be adapted to expedite the loading of the gun; and it is not difficult to make a mechanical arrangement by which the shot and cartridge shall be lifted up to the gun, inserted, and rammed home, at a rate far exceeding anything that can now be done by hand; and as the weight and clumsiness of the gun, the carriage, and machinery are of no object, I think I can make a breech-loading gun capable of carrying 12-inch solid shot with a full charge, which may be loaded and discharged at the rate of two or three per minute; but the principle of mounting a gun in such a float is equally applicable to a common gun, which might still be loaded mechanically.