Page:Our big guns.djvu/30

( 24 ) while the "three-decker" the Duke of Wellington, whose screw-propeller trials I well remember taking place when I was engaged in conducting other screw-propeller trials at Portsmouth, in the year 1853, a vessel of only 6070 tons displacement, had an armament of 131 guns, the largest of which, however, was, I believe, only a 32-pounder, and, if so, weighed no more than 56 cwt.

Now we have shown, that in order to obtain good duty out of the metal employed, the outer metal of the gun must be subjected to an initial tensile strain, and that, pending the solution of the wire gun question, that strain must be given by hooping. The question next arises, what metal shall we use? I leave out of consideration, for our purposes of to-night, various metals that are from time to time proposed, because they are still in the experimental stage, and the duty of those charged with providing the nation with its means of defence, is to employ for service, only those materials, and those systems of construction, which have passed that stage.

Under this condition of things the gun-constructor finds himself called on to select from cast iron, from wrought iron, and from steel. Having regard to the work which the rifling has to perform, and to other considerations, steel is clearly the metal that one would desire to employ for the central tube. As regards the hoops, one would not be inclined to suggest cast iron, and there remain, therefore, only wrought iron and steel. For a considerable period wrought iron was used for this purpose, and very well it did its work; made as a very long bar, and coiled into a helix of the desired dimensions, the successive convolutions were welded together at one operation, and in this manner the desired cylinder, or jacket was forged, having the grain of the iron running round about it in the best direction, for acting as a circumferential reinforcement to the tube.

But some few years since, after much investigation and after consultation with steel manufacturers, it was determined to use this material for all parts of the gun.

I must now ask your attention for a short time to the subject of steel.