146 Mr. Mallet on the Physical Conditions 



divided by other fractures in planes more or less completely at right angles to 

 the preceding one, and by several " turn out," or transverse fractures. These 

 latter occur and are more numerous in proportion as the metal of the gun is 

 harder, more highly elastic, and more rigid, and as the bursting charge is more 

 powerful ; in a word, the fragments are smaller and more numerous and irre- 

 gular when the rending forces, are greatly in excess of the resisting powers of 

 the metal. Wrought-iron and steel guns fracture much in the same way, but 

 the fractures of bronze guns are of a somewhat different character, and the 

 fragments are bent and distorted, both, owing to the greater toughness and 

 ductility of the material. 



8. Three circumstances are specially worthy of attention, as indicated by the 

 lines of fracture thus generally described: — 



1°. The dividing longitudinal plane, whether vertical or 

 horizontal, is always found to assume a sudden curved form, 

 as in diagram, at one or other side near the exterior of the 

 gun; indicating that \}\e fracture begins at one side, s (that 

 opposite to the inflected fracture) ; and that fracture has 

 spread from that side, the gun opening out, and the divided 

 surfaces turning from each other upon the point of inflec- 

 tion at/. 



2°. Fracture, therefore, appears in all cases to commence at the interior of 

 the chase, and to propagate itself outwards, thus rending the metal from within 

 to without — a result which, though difficult at first to reconcile to the imagina- 

 tion, is pointed to by every mathematical investigation, of the resistance of 

 cylinders to internal fluid or elastic pressure, leading to whatever formula, since 

 the metal must yield first, where the pressure per square inch is greatest upon its 

 resisting unit of section, and this is in the interior of the thickness. 



3°. The planes of fracture follow the track, with almost unerring pre- 

 cision, of all re-entering angles, and of all sudden changes of scantling or 

 dimension, however trifling, in the external contour of the gun. Thus a 

 vertical longitudinal fracture often passes through the vent (as being the 

 weakest part in section), but much more frequently follows along the re- 

 entering angle made by the exterior of the gun at its meeting with one or 

 other side of the vent-field, as in Fig. 1 and Fig. 3. The transverse fractures, 



