﻿ON coxstri'ctinct cannon of great caliber. 11 



and the parts ■which they siuTomid, considerably more than yoVoth part of a diam- 

 eter. The fixing the hoops in their places by the screw, or some equivalent, is ab- 

 solutely necessary, not merely to reinforce the body against cross fracture, but to 

 prevent them from starting with every shock of the recoil. I know, by experiment, 

 that the screw-thread will fix them effectually. The trunnions must, of course, be 

 welded upon one of the hoops, and this hoop must be splined, to prevent its turning 

 by the recoil. Small splines should likewise be inserted under every hoop. It will, 

 moreoA-er, be advantageous to make the threads of the female screws sensibly finer 

 than those of the male, to draw, by the shrink, the inner rings together endwise. 



It will be seen that, with a gun made in this way, we must depend upon the cast- 

 iron body to resist the strain tending to produce cross fracture, though this resistance 

 will be in some degree supported by the outer rings breaking joint over the inner 

 rings. But if the body be made to constitute half the thickness of the walls, it will 

 be found sufficient for the purpose without any reinforcement from the rings. This 

 residts from a principle or law, which, so far as I know, was first published by me 

 in the vear 1845, in a pamphlet on wrought-iron and steel cannon. As I cannot now 

 put this matter in a better form than that in which I have there given it, I will here 

 quote the statement as then made. 



" Let us suppose that we have a hollow cylinder, say twelve inches long, the cal- 

 iber being one inch in diameter, and the walls one inch thick, giving an external 

 diameter of three inches. Suppose this cylinder to be perfectly and firmly closed, at 

 its ends, by screw plugs, or any other sufficient means. Let this be filled with gun- 

 powder and fired. The fluid will exert an equal pressure, in evei-y direction, upon 

 equal surfaces of the sides and ends of the hollow cylinder. Let us next examine 

 the resisting power of a portion of this cylinder, say one inch long, situated in the 

 middle, or equally distant from the ends, so that it shall not be strengthened by the 

 iron which is beyond the action of the powder. The fluid enclosed by this ring of 

 one inch long contains an area of one square inch, if a section be made through it in 

 the direction of its axis ; and the section of the ring itself, made in the same du'ection, 

 will measure two square inches. We have then the tenacity or cohesive force of two 

 square inches of iron in opposition to an area of the fluid measuring one square inch ; 

 and if we take the tenacity of the iron at 65,000 pounds, the cylinder will not be 

 bui-st, in the direction of its length, unless the expansive force of the fluid exceed 

 130,000 pounds to each inch. Next, let us suppose a section made through the cylin- 

 der and fluid, transversely. The area of the fluid, equal to the square of the diame- 

 ter of the hollow cylinder, is one cucular inch, and the area of the whole section, the 



