ON THE CONSTRUCTION OP HOOPED CANNON. 61 



upon the opposite surface. The principal ohje lion to this moth* of cramping 

 or interlocking the surfaces will he found in the nei y of heating the hoop 

 to a much higher temperature than is required with the screw-thread, in order 

 to expand it so that it may pass to its place upon the gun. Then prominences 

 and grooves, doubtless, might serve a better purpoee then t lie mere rough n< 

 left by the turning tools, as now often used. 1 am confident, however, that 

 no device can be made, superior to the ■crew-threads, and nothing belter than 

 this is needed. 



The benefit, moreover, to be derived from making "the threads of the 

 female screws sensibly finer than those of the male," must, I think, be cvideat 



after a little examination. By making this difference the x^V^ <n P ar ^ or P cr * 

 haps a little more (that is, by making 1000 turns of the spiral of the female 

 to occupy a shorter space upon the hoop by a y^^th part than the seine 

 number of turns do upon the body), they will be more marly equal when the 

 hoop is expanded by heat, than if they had been formed of equal finer or 

 pitch. The hoop will, therefore, go more readily to its place when expanded, 

 from bearing this finer thread. When the first layer is shrunk in its place, 

 each hoop will be under a lengthwise strain ; and, again, when the second layer 



is shrunk upon the first, the first layer, and, under it, the body of the gun, 

 will be drawn together lengthwise, and thus the body will be guarded from 



cross-fracture, as it is guarded from longitudinal fracture by the circumferential 

 strain of the same hoops. 



Having thus exhibited the principles which should direct us in the con- 

 struction of hooped cannon, and the experiments by which these principles are 

 come at, I now proceed to describe the method of forging the hooj , and of 

 giving to them that combination of hardness, elasticity, and tenacity, which has 

 been shown to be so important to the strength of the cannon. 



To construct one of the hoops for a cannon of the size before mentioned, 

 that is, of 14-inch caliber, the hoop having, when finished, 27.972 inches' internal 

 diameter, and being 3£ inches thick, and 15 inches long (or broad), I take a 

 flat bar, say 14 inches wide, from half an inch to an inch thick, and of such 

 length that, when wound into a coil, it shall form the thick ftCff required for 

 the hoop, after allowing for the waste in welding, forging, and finishing. After 

 its ends have been scarfed to a long wedge form, it is to be heated to a low 

 red heat, and then wound upon a cylinder of say 25 or 26 inches diameter, as a 

 ribbon is wound upon a block. Next, it is to be heated in a proper furnace to 

 a good welding heat, and then, being placed upon an arbor, or mandrel, of 



VOL. IX. NEW SERIES. 9 



