144 Mr. Mallet on the Physical Conditions 



guns cast in one mass the external portions of the metal are far from bearing a 

 proportional share of the strain. The pressure per square inch, whatever it may 

 be, acts most powerfully upon the internal lamina of the bore, and when the 

 pressure is very great, and the difference between D' and D" is very great also, 

 the limits of elastic extension are passed as respects the metal of the internal 

 portions of the gun, and these are torn before any proportionate strain is visited 

 on the outer portions. The strains producing inceptive rupture being of the 

 nature of impulsive forces acting upon imperfectly elastic material, it always 

 happens that a rent commenced, is followed (without any appreciable interval 

 of time) by the flying to pieces of the whole gun. 



6. Accidents of the most fatal character, resulting from the bursting of 

 heavy iron guns, have been frequent of late years, especially of that class 

 known as " shell guns," whose proportions unfit them generally for throwing 

 solid shot: as for example, a 10-inch gun, of 10 feet 6 inches long, of 116 cwt., 

 which burst at Shoeburyness on the 18th June, 1852, in firing a hollow shot 

 of 110 lbs., with a charge of 16 lbs. of powder, at an elevation of 32°, killing 

 several men ; and another similar, but more fatal, accident, which occurred at 

 Gibraltar ; while others have taken place under the destructive conditions due 

 to the confined space between decks in men-of-war. 



These accidents have principally occurred to 10-inch and 8-inch guns, and to 

 68 and 32-pounders of iron; and in solid-shot gims, chiefly either in very rapid 

 firing, or in firing red-hot shot. 



One of the main objects at present in view is to point out some circum- 

 stances affecting the destruction by bursting of cast-iron guns under such con- 

 ditions, which appear so far to have been unnoticed or misunderstood by 

 artillerists — namely, the effects of unequal or local expansion produced by 

 local inequality of temperature, whether arising from the heating of the gun 

 internally by red-hot shot or by " quick firing," — in powerfully increasing the 

 strain, upon the metal, due to the discharge. 



In the progress of the investigation leading to this result, however, I shall 

 have occasion, incidentally, to treat of most of the important conditions of a 

 physical character that affect the proper design and construction of artillery, of 

 whatever magnitude, as well as to point out the chief circumstances upon 

 which failure depends. In fulfilling my original object, therefore (if success- 



