﻿OS COXSTRUCTIXG CANNON OF GREAT CALIBER. 13 



pounds for the strength of the casting, to each inch of its length. The first hoop has its 

 strength reduced from 1 to a mean of .8. Take the strength of wi'ought-u'on at 60,000 

 pounds to the inch, and we have 60,000 X .8 = 48,000 poimds to the inch. The 

 thickness, of both sides, is 7 inches, and 48,000 X 7 = 336,000 pounds. The outside 

 rmg must be reduced in strength by the same rule, for its mean, from 1 to .832, which 

 gives it 49,920 pounds per inch, and for the 7 inches 349,440 pounds. We have then, 

 for each inch in length, 



Cast-u-on body of the gun ..... 210,000 pounds. 

 Inner wrought-u-on hoop ..... 336,000 " 

 Outer wrought-iron hoop ..... 349,440 " 



895,440 pounds. 



The diameter of the bore being 14 inches, we have ^-^ il'"' = 63,960 pounds, as the 

 resistance to oppose to each square inch of the fluid from the powder. The gun 

 will bear, then, a pressure of 4,264 atmospheres. 



The resistance to cross fracture at the part nearest to the breech will be, from the 

 cast-iron, 28^ — 14^ = 784 — 196 circular inches, equal to 460 square inches. Cohesive 

 force, unreduced, 30,000 poimds, and 30,000X460 = 13,800,000 pounds, the whole 

 strength. The bore contains 153 square inches, and -^^-1:^3^^^ ^ 90,196 pounds to 

 resist each square inch of the fluid, or 26,236 pounds to each square inch more than 

 is provided to resist the longitudinal fracture ; and this excess will be further reinforced 

 by the wrought-ii'on rings, which, being screwed upon the casting, and the outer layer 

 breaking joint over the inner, wUl add to the resistance to a great amoimt, which how- 

 ever need not be computed. 



Let us now examine a gim made of a single casting of the dimensions that are 

 given above; that is, of 14 inches' bore, and sides 14 inches thick. Taking the normal 

 strengtli of cast-iron as before at 30,000 pounds per inch, we must reduce it, accord- 

 ing to the laws before explained, to one third, or a mean of 10,000 pounds per inch ; 

 and the thickness of both sides being 28 inches, we have 10,000x28 = 280,000 

 pounds for the whole strength, and ^^H"" = 20,000 pounds to each inch of the fluid 

 pressure, or 1,333 atmospheres, or iUii, or less than one thii'd of the first example. 

 Against a cross fr-acture the cast gun wUl possess a great excess of strength, which I 

 do not like to call useless, although I do not perceive how it can be of any essential, 

 practical advantage. 



Let us next inquiie, "What force is requu-ed to give a ball of 14 inches' diameter a 

 velocity of 1,600 feet a second ? "\Ve shall obtain a better conception of this force by 



