involved in the Construction of Artillery. \^\ 



the fracture took place all round, along the plane of junction of the contermi- 

 nous crystals formed perpendicular to the external and internal surfaces of the 

 bottom and of the sides of the cylinder, proving that such planes of junction 

 where, as in Fig. 2 and 3, the crystals join and interlace confusedly, are 

 planes of trml'wes.s— planes in which the cohesion of the metal is less and less 

 for this reason, than in any other parts of the mass. These lines of weakness 

 extend from v to v throughout all the figures. The form of the bottom of 

 this cylinder was changed by Mr. Stephenson, from a distinct appreciation of 

 the fact that the fracture of the part was in some way connected with the sharp 

 and sudden termination, square to the axis of the cylinder, though without 

 apparently any clear conception of the crystalline laws upon which the fact 

 depended ; and a new cylinder with a sort of semiovoidal end was made— 

 a section of a portion of which is represented in Fig. 6. This stood the strain 

 uninjured. Here the principal axes of the crystals all are directed, as in Fisrs. 

 1 and 4, to the centre. They, therefore, gradually change their direction, and 

 no planes of weakness are produced. (Note F.) 



19. It is to be hoped that these illustrations have served to make clear the o-e- 

 neral law as applied to cast-iron artillery— that every abrupt change in the form of 

 the exterior— every salient, and every re-entering angle, no matter how small, upon 

 the exterior of the gun or mortar is attended with an equally sudden change in 

 the arrangement of the crystals of the metal, and that every such change is accompa- 

 nied with one or more planes of weakness in the mass. 



20. Figs. 7 and 8 are sections of portions of a large cast-iron gun. The 

 former, part of the breech, through the " vent-field" square to the axis of the bore ; 

 the latter, a section near a trunnion, also square to the axis. Fig. 9, a section 

 of a reinforce ring in the plane of the axis. In all of these are'^shown, in an 

 exaggerated form, the directions of crystalline aggregation, and the pknes of 

 weakness resulting from it. 



21. It will be remarked that the square projection of the "vent-field" pro- 

 duces at each angle planes of weakness, which, in the case of the re-entering angles 

 penetrate deep into the thickness of the gun ; and that these planes really dJ 

 exist IS evidenced by referring back to Plate No. i, in which it will be seen 

 that the lines of fracture in burst gims almost always follow alon<^ the angle at 

 the sides of the " vent-field ;" so also in the case of the trunnions, Fig. 8. On 



X 2 



