involved in the Construction of Artillery. 145 



ful), a treatise on the Construction of Artillery has resulted, embracing many 

 views of not a little interest to science, and, as I believe, new to both the science 

 and the practice of the gun-founder. 



2. — Directions of Fracture in Burst Guns. 



7. Before entering further upon the subject, however, it may be desirable to 

 explain briefly the lines or directions of fracture assumed by all heavy cast-iron 

 guns that are sound, when burst; and to point out some properties due to the 

 molecular or crystalline structure of cast-iron, upon which in part such lines 

 of fracture depend, and upon a due regard to which the strength or weakness 

 of cast guns much depends. In doing so, I shall have occasion to notice, 

 though too briefly for the importance of the subject, several circumstances and 

 conditions bearing directly upon the gun-founder's art, which, so far as I know, 

 have not hitherto been treated of in a determinate manner by any previous 

 writer. 



The Plate No. i. shows by the heavy dotted lines the almost invariable 

 directions in which fracture takes place when cast-iron guns burst in proof or 

 in service, assuming no serious flaw or other defect to exist anywhere. The 

 gun splits up nearly into equal halves, usually by a vertical or nearly vertical 

 plane, passing through the axis of the piece, and extending from the breech ring, 

 which it often also divides, longitudinally to a point a little in advance of the 

 trunnions, where it turns out to one side and to the other, leaving the muzzle 

 portion of the gun, for a length of between f and ^ its whole length un- 

 broken. This portion of the gun at the moment of fracture is thrown forward, 

 partly by the direct action of the powder blast in escaping, partly through the 

 imbalanced action of the elastic forces within the strained metal suddenly re- 

 leased, and partly by the friction of the passing-through shot. It usually falls 

 to the ground with the muzzle end foremost ; and as this strikes the ground 

 the mass throws a somerset, and is found lying along, in the line in which 

 the gun had been trained, but with the direction of the muzzle reversed, or 

 pointing backwards; a circumstance often remarked upon with surprise by 

 artillery ofiicers, but, thus easily accounted for. 



Sometimes the portions of the gun at, and in rear of, the trunnions are 



