ARTILLERY 237 



it in masses sufficiently large without the occurrence of flaws, which, in/ the great 

 majority of cases, would destroy its efficiency. Sheer-steel may be forged, like 

 wrought-iron, into large pieces : but in a gun made from a solid mass of either of 

 these substances, the full strength of the material can never be realised, because the 

 tenacity of wrought-iron or steel is always less in the lateral than in the longitudinal 

 direction : and it is the lateral strength which, in a gun so manufactured, would be 

 chiefly brought into action. There is also much uncertainty in the lateral strength 

 of wrought-iron or steel, because the flaws or imperfections of welding which exist 

 in all thick masses of those materials almost invariably run in the direction of the 

 length, and in general, therefore, only detract from the strength in the transverse 

 direction. It is for these reasons that the barrels of muskets and sporting guns are 

 formed by twisting long slips of iron into spiral tubes, and then welding together the 

 edges, by which means the longitudinal strength of the slip becomes opposed to the 

 explosive force of the powder, and the weldings being transverse with the bore, have 

 no important influence in lessening the strength of the barrel. It is also to be ob- 

 served, in reference to the strength of steel or wrought-iron cannon, that the resistance 

 of a cylinder to internal pressure does not increase in the ratio of its thickness. If 

 the cylinder be regarded as made up of a number of concentric layers, each capable of 

 sustaining without injury a degree of extension proportionate to its length, it is obvious, 

 that the greater the circumference of each layer, the less will it be stretched by a given 

 distention of the bore, and, consequently, the less will it contribute to the general 

 strength of the cylinder. The ratio of this decrease is very rapid, being as the 

 square of the circumference, or distance from the centre inversely ; and, consequently, 

 when the cylinder is thick, the deficiency of strength from this cause becomes very great. 



' Now this defect can only be remedied by giving to the external portion of the 

 cylinder a certain initial tension, gradually decreasing and finally passing into com- 

 pression towards the centre ; and although this condition cannot be effected by any 

 known process of forging or casting, yet where wrought-iron or steel is the material 

 used, it may in a great measure be attained by shrinking an outer cylinder upon an 

 inner one, and in like manner superadding others until the requisite thickness has 

 been acquired. 



1 The method, however, of forming steel or wrought-iron guns, by simply forging 

 the material into the required form, and boring it in the usual manner, was so much 

 recommended by its facility, that I was induced to make some experiments to test its 

 sufficiency. 



' With this view a number of cylinders were forged, each twelve inches long and 

 five inches in the outward diameter. These were bored to an internal diameter of 

 one and three-quarter inches, and tested in the following manner : Each cylinder 

 was entirely filled with gunpowder, and the open end was pressed by screws against a 

 very thick iron tube bored to the same diameter, and containing a cylindrical shot of 

 lead equal in weight to about three spherical shot of the same diameter and material. 

 Several of the cylinders burst on the first discharge, and those which remained un- 

 injured were afterwards reduced in thickness, and tested a second time. If they still 

 resisted the explosion, the thickness was further diminished ; and this mode of pro- 

 ceeding was continued until fracture took place in ail of them. 



' The results obtained in this manner showed, as had been apprehended, great un- 

 certainty in the strength of the material, and rendered it impossible to define the 

 thickness necessary to resist a given charge of powder. I felt compelled, therefore, to 

 dismiss this mode of construction, and to adopt another more correct in principle, but 

 more difficult of execution. 



' In the above experiment it was found that steel was more subject to defects of 

 welding than iron ; but being a harder substance, and therefore more fitted to form 

 the surface of a bore, I determined to apply it as an internal lining, and to obtain the 

 necessary strength by encircling it with twisted cylinders of wrought-iron, tightly 

 contracted upon the steel core by the usual process of cooling after previous expan- 

 sion by heat. Considerable difficulties were encountered in carrying this plan into 

 practice ; but I ultimately succeeded in completing a gun, of which the following is 

 a description. 



The gun, when fired, recoils upon an ascending slide without displacing the 

 carriage, and then returns to its place by gravity. The slide-frame turns upon a 

 pivot, which permits the gun to be pointed to either side without moving the carriage. 

 The gun is elevated and depressed by means of a screw, which is fixed to and moves 

 with the slide, and a similar screw is applied for the traversing or horizontal move- 

 ment. The arrangement for loading at the breech may be described as follows : At 

 the back end of the gun a powerful screw is applied, having a hole through the centre, 

 forming a prolongation of the bore, and through which hole the bullet and charge are 

 delivered into the gun. A ' breech-piece ' with a mitred face, fitting a similar faco 



