MECHANICS AND USEFUL ARTS. 55 



teen-inch calibre constructed at the Mersey Company's works, which has 

 successfully withstood some severe trials, though even this gun is not a per- 

 fectly sound forging throughout. This want of success is ascribed partly to 

 the difficult} 7 of ensuring perfect welds throughout a very large forging, 

 and partly to a change which is graduallj 7 effected in the physical structure 

 of the metal by its repeated exposure to a high temperature, and possibly, 

 also, in some measure, by its frequent subjection to powerful concussion. 

 In large masses of wrought iron, which have been built up by welding, the 

 fibrous structure of the metal is always found to have passed over, more or 

 fess perfectly, into a lamellar structure, and the strength of the mass thus 

 becomes very considerably diminished. 



While unsuccessful attempts to construct cannon of large masses of mal- 

 leable iron were still in progress, Mr. Mallet, Captain Biakeley, and others, 

 who had given the subject of the construction of cannon of large size their 

 serious attention, and had applied mathematical reasoning to its elucidation, 

 had arrived at the conclusion that the true system to be followed was that 

 of constructing cannon of several parts, combined in such a manner as to 

 render every portion of the metal available in resisting, by its tenacity and 

 elasticity, the strain exerted upon the gun by the explosion of powder. The 

 method of construction proposed by those gentlemen consisted in preparing, 

 in the first instance, cylinders (or rings, to be afterwards braced together), 

 and in shrinking upon these other rings, of which the internal diameter was 

 somewhat less than the external diameter of the first rings or the cylinder. 

 The latter are thus placed in a state of compression, while the external rings 

 are in a state of tension. Other rings are again shrunk upon the outer ones, 

 according to the size of the gun and the strain which it has to bear. In this 

 way the whole of the metal composing a heavy gun or mortar is arranged 

 in a condition most favorable to the effectual resistance of a sudden strain 

 applied from the interior. A gun constructed on this plan, by Captain 

 Biakeley, has exhibited very great enduring powers. Two enormous mor- 

 tars have also been constructed by Mr. Mallet on the same principle; and, 

 although the trials with one of these were only partially successful, the cor- 

 rectness of the principles above referred to were in no way impugned by the 

 results obtained. 



The methods adopted for the production of the beautiful rifle-gun invented 

 by Sir William Armstrong, which is rapidly replacing the old bronze field- 

 guns, afford an interesting illustration of the application of the above sys- 

 tem to the construction of very light and dm-able cannon. This gun consists 

 essentially of rings partly welded together, so as to produce a cylinder or 

 barrel of sufficient length, and partly shrunk one upon another, so as to im- 

 part the requisite strength to the structure. The rings themselves are from 

 two to three feet in length, and are formed out of long bars, which are coiled 

 up, when at a red-heat, into spiral tubes, and afterwards Avoided into solid 

 rings or tubes by a few blows from the steam-hammer, applied to one end of 

 the heated coil, while in a vertical position. The rings are united, to form 

 the ban-el of the gun, by raising to a welding-heat the closely proximate 

 extremities of two rings, placed end to end, and then applying a powerful 

 pressure to the cold ends of the rings. In the large guns, a second layer of 

 rings is shrunk on to the first set, or barrel, throughout the length; but in 

 the smaller guns it is only behind the trunnions that two additional rings are 

 shrunk on, one over the other. The outer ring is exactly like those already 

 described ; but the intermediate one is prepared by bending two iron slabs into a 



