174 ANNUAL, OF SCIENTIFIC DISCOVERY. 



instant of its flight, to strike, the upper surface of the bore, where a second 

 indentation is made, considerably in advance of the first, and from this a third, 

 still more advanced, upon the under side. These indentations go on increasing 

 in number and size, and at length bulges appear upon the outside of the gun, 

 which becomes oval near the muzzle, and is at last destroyed. 



The lodgment here described has been attributed wholly to the downward 

 pressure of the fluid when escaping through the opening of the windage, 

 which is all upon the upper side of the ball, the under side resting by its 

 weight in contact with the bore. There must undoubtedly be a great escape, 

 not only of the fluid, but of burning powder in grains, through this passage, 

 and the downward pressure from these causes may present an excess over the 

 opposite pressure of the powder upon the under side of the ball, capable of 

 producing some impression upon the under surface of the bore. I am inclined, 

 however, to attribute the indentation mostly, if not entirely, to the compression 

 of the back hemisphere of the ball under the enormous blow of the explosion, 

 producing a corresponding enlargement of the bail in its diameter transverse 

 to the axis of the bore. The smith produces such a change of form in his bar 

 of iron, at pleasure, by the blows of a sledge applied to its end. The operation 

 is called upsetting. This enlargement must impress itself upon the part of the 

 bore upon the under side upon which the shot rests, and is alone sufficient, in 

 my mind, to account for the whole mischief. 



This view of the subject is confirmed by the form of the lodgment, which 

 consists, at first, of a single narrow impression, exactly corresponding to a 

 very small segment of the ball, and not in the least in advance of the spot on 

 which the ball rests before the discharge. JSTow this would be the exact form 

 and place of an impression produced by a sudden enlargement of the ball, afid 

 an equally rapid recovery of its true figure, which it would derive from its 

 elasticity. But if the lodgment were produced by the pressure of the fluid 

 upon its upper surface, it ought to form a long groove or channel, ceasing only 

 with the diminished pressure of the fluid near the muzzle. Furthermore, the 

 lodgment is greatest when a hard oakum wad is used behind the ball. Now 

 such a wad must prevent, in some degree at least, the escape of the fluid, and 

 therefore diminish the downward pressure. But such a wad driven hardest 

 against the middle of the ball, in its rear, would act most advantageously to 

 produce the lateral enlargement by upsetting it as before described. 



Hard cast-iron guns do not exhibit this indentation in so great a degree, 

 because, being unmalleable, they are incapable of a permanent change of form 

 without fracture. With them, therefore, this pounding of the ball, being 

 repeated a few hundred times, shatters the walls of the gun, which at length 

 gives way at once and goes to pieces. 



It must be obvious, that, if the lodgment be attributed to either or both of 

 the causes which I have recited, it may be prevented by a most simple and 

 easy means. This is nothing more than providing that the ball shall, at the 

 moment of the explosion of the powder, have no part in contact with the bore 

 of the gun, but that the windage space shall be equally distributed about the 

 whole circumference. This may be entirely secured by enveloping the ball in 

 a bag made of felt, or of hard woollen cloth, having an additional patch upon 



