ON RECOIL. 191 



is repulsion among the atoms when assuming the form of air. 

 The force of repulsion does not operate by a single impulse, 

 but through a repetition of impulses, or a continued action, 

 of which the effect is accumulated in the inertia of matter ; 

 thus, all great velocities are tJie terminations of an accelerated 

 motion. As in every case of repulsion, two objects at least 

 must be concerned, there can be no motion or action 

 without a concomitant or opposite motion or reaction ; it is 

 therefore clear that the one must be repelled just as much as 

 the other, although with a difference of velocity proportioned 

 to the difference of size. The extraordinary action of gun- 

 powder on the shot, the barrel, and the fore part of the 

 stock, although appearing so sudden, is not an instantaneous 

 but a gradual and therefore accelerating action ; so is the 

 recoil or reaction of the back part of the gun. The action 

 or movement of the charge commences comparatively slowly 

 at first, so does the reaction or recoil. The action of the 

 charge and gradual increase of the gas, all along the barrel, 

 is the cause ; the action of recoil is the effect. The cause 

 begins with the first movement of charge, and ends with the 

 charge leaving the barrel. The retardation of the shot in 

 passing up the barrel and the acceleration of the recoil take 

 place within so short a time that it is not apparent to our 

 senses, and, therefore, to some may appear momentary ; but 

 the mind perceives the nature of the phenomenon as dis- 

 tinctly as if a large ball were rolled against the end of a long 

 steel spring, and thrown back again from it. 



" For the same reason that all great velocities require con- 

 tinued action or repeated impulse to produce them, so do they 

 also to destroy them the inertia of motion and of rest being 

 exactly equal. The perfection of machinery depends much 

 on diminishing among the moving parts the resistance which 

 arises from friction. The explosion of gunpowder being a 

 repulsion among the atoms when assuming the form of 

 air, its greatest efficacy would be destroyed if the shot 

 were prevented by unnecessary friction from starting gra- 

 dually on its course with the very slightest force which 

 first affects it. Even such apparent trifles as certain unguents 

 increase, and others decrease the friction of quiescence that 

 is, increase or diminish the force requisite to produce the 



