THE PROPERTIES
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ting the gun they are still impelled by the elastic fluid; or,in other words, when arrived at the mouth of the piece,their velocity is less than that of the fluid itself.
80. The action of the elastic fluid on the shot in movingalong the bore of the gun is so powerful at the beginning ofthe movement, that the range from a small charge some-times equals, and even exceeds, that from a larger charge,though they both take fire before the sliot begins to move.This is owing to the small charge occupying a less space ofthe bore; whence the shot is longer impelled by the fluid, asit has a longer space to move through in the gun. To elu-cidate this, let an experiment be made with a gun a diameterand half of its shot in length; the ranges, or the penetrationsof the shot into soft earth, will be greater when the chargeoccupies half, than when it occupies a whole diameter.Thus the decrease of range in a piece of ordnance that is over-charged arises not only from the greater weight of matterto be impelled by the fired powder, but also from the lessspace that the shot has to pass through in the piece, and theless impulsion of the elastic fluid.
81. From these premises, it will be easy to explain, why,in fire-arms loaded in the common manner, only a certainquantity of powder can take fire.
There are two actions to be distinguished in the fluid ge-nerated at the burning of powder; of fire, and elasticity. Asthe fluid separates, and disengages itself from the burninggrains, it carries off with it different inflamed combustibleparticles ; the degree of fire is then weakened, as much fromits expansion, as from the extinction of the flame, owing tothe destruction of these combustible particles: wherefore thefluid, at a certain distance from the burning grains, doesnot contain heat sufficient to inflame other grains; but itselasticity, though weakened by the decrease of heat, does notcease to act against the sides of the containing vessel. Nowas the inflammation of powder in fire-arms commences atthe vent situated at the bottom of the bore, there is generatedfrom the first grains an elastic fluid, which insinuates itselfinto the interstices of the other grains; but the more this fluidexpands, and the combustible particles mixed with it are de-stroyed, the heat becomes less intense, and unable to fire thegrains more distant from the vent: but a fresh fluid is suc-cessively generating, and inflaming those which the first pro-duced fluid had not power to inflame 3 the quantity of the