22 SHOOTING. 



arise on_ discharging a gun loaded with powder confined by a cylin- 

 drical piece of wadding, and having its muzzle filled with clay, or 

 some other substance, offering a moderate degree of resistance. In 

 such a case, the first effect of the explosion is to produce an enor- 

 mous pressui-e on everything confining it, and to advance the 

 wadding thi'ough a very small space. Here_ let us consider_ it as 

 at rest for a moment, and examme its condition. The portion of 

 air in immediate contact with the wadding is condensed, and if the 

 wadding were to remain at rest, the air throughout the tube would 

 soon acquire a uniform density. But this would require a small 

 interval of time, for the condensation next the wadding would 

 travel with the velocity of sound to the other end, fi'om whence, 

 being reflected back, a series of waves would be generated, which, 

 aided by the friction of the tube, would ultimately destroy the 

 motion. But until the first wave reaches the impediment at the 

 muzzle, the air can exert no pressui-e against it. Now, if the 

 velocity communicated to thp wadding is very much greater than 

 that of sound, the condensation of the air immediately in advance 

 of it may be very great before the resistance transmitted to the 

 muzzle is at all considerable ; in wliich case the mutual repulsion 

 of the particles of the air so compressed vidll offer an absolute bar- 

 rier to the advance of the wadding. If this explanation be correct, 

 additional recoil when a gun is loaded with small shot or sand, may 

 arise in some measure from the condensation of the air contained 

 between their^ particles, but chiefly from the velocity communicated 

 by the explosion to those particles of the substances in immediate 

 contact with the powder being greater than that with which a wave 

 can be transmitted through them. It otherwise affords a reason 

 for the success usually attending the blasting of rocks. That the 

 destruction of the gun-barrel does not arise from the property pos- 

 sessed by fluids, and in some measure also by sand and small shot, 

 of pressmg equally in all directions, and thus exciting a force 

 agamst a large portion of the interior surface, seems to be proved by 

 a circumstance mentioned by Le Vaillant and other travellers, that, 

 for the purpose of taking birds without injuring their plumage, 

 they filled the barrel of their fowling-pieces with water, instead of 

 loading them with a charge of shot. The same reasoning explains 

 a curious phenomenon which occurs in firing a still more power- 

 fuUy-explosive substance. If we put a small_ quantity of ful- 

 minating silver upon the face of an anvil, and strike it slightly with 

 a hammer,_ it explodes • but instead of breaking either the hammer 

 or the anvil, it is found that that part of the face of each in contact 

 with the fulminating silver is damaged. In this case, the velocity 

 communicated hj the elastic matter disengaged may be greater 

 than the velocity of a wave traversing steel ; so that the particles 

 at the surface are driven by the explosion so near to those next 

 adjacent, that when the compelled force is removed, the repulsion 

 of the particles within the mass drives back those nearer the sur- 

 face "With such force that they pass beyond the Limits of attraction. 



