involved in the Construction of Artillery. 377 



say, 50'5 inches area, and the length of trajeot of the shot to have been 8 feet, we shall find 

 that the maximum pressure per square inch upon the gun could not have been much less 

 than sixfold the ultimate coefficient of rupture for cast-steel ; yet even this enormous strain 

 a bronze gun might possibly have withstood for a moment with no more damage than 

 enlargement of bore; but expose the rigid steel gun to a strain, but for an instant, greater 

 than its ultimate cohesion for continuous force, and fracture results. 



This example, then, though not conclusive, from the want of provision that appears to 

 have attended it, fully indicates the faithless nature of this rigid material, where its re- 

 sisting powers and tlie forces acting upon it, are at all nearly balanced. 



The immense excess of bursting force exercised upon this gun, over and above that 

 merely necessary just to rupture it, is evidenced by the irregular and curved lines of the 

 fractured fragments, which are only found to follow the directions indicated (in Chap. 2, 

 text), in sound guns, exposed to bursting strains not greatly in excess of their resistances. 

 This is very satisfactorily shown by comparing the numerous diagrams of fractured guns in 

 the experiments made at Gavre, in 1836 (Correard, Paris, 1837, 8vo), and those of the 

 " United States Reports" (Triibner, London, 1856, 4to), on Columbiads and other heavy 

 guns. 



The occasional apparent departure of the lines of fracture, from tlic lines of re-entering 

 angles on the external contour, or other directions indicated in the text, is not, therefore, 

 any disproof of the correctness of the views there advanced, but a consequence of great 

 excess in the bursting power, which always produces angular, knife-edged fragments and frac- 

 tures, in irregular curved lines, crossing each other, from causes not difficult to artalyze. 

 The fracture of steel is, however, always more of this character than that of cast or wrought 

 iron. 



I am informed a 12-pounder steel gun, at Vincennes, has been fired more than 2000 

 rounds, without showing any symptoms of injury, except enlargement of vent. — since 

 bouched with copper; and that it is intended to proceed with 6ring it up to 10,000 rounds, 

 if practicable. 



\( ii'iili a large excess of strength, there can be no apprehension that it will not stand this 

 test. 



Note Q.— (Sects. 206 and 214.) 



On the 12th July, 1855, a wrought-iron 8-inch gun was proved at Woolwich, and burst 

 into several pieces at the first discharge. 



This gun was forged at the Gospel Oak Works, Shropshire, and was proportioned in 

 length and scantling very nearly by the established cast-iron models, for the same caliber 

 and class of grun. 



