OF GUN-POWDER. Zy

has to move through in the piece. This strews clearly* thatthe ranges or the initial velocities of Jhot impelled from gunsere proportionally less than the recoils , and that if the chargebe augmented to a certain point, the ranges will diminish,while the recoils will increase.

93. Thus, very large charges should never be used in theservice of artillery, as the ranges from them are shorter, or atmost but equal; and beside the useless expenditure of pow-der, the carriages are soon rendered unserviceable, and thegreater part of the shot are of no effect.

94. The causes of the recoil merit a more particular exa-mination. There are two motions in the breech of a'gun,at the instant of discharge ; one up and down, by which itsinks into the coins, and sometimes throws them upon theground, if too obtuse or improperly placed : this reflectedmovement of the breech takes place when the center of gra-vity of the gun is too near to the axis of the trunnions, orwhen the coins are made of too elastic a substance. Theother is an attempt to retire with all the machine in a di-rection opposite to that of the movement of the shot, whichis termed the recoil.

95. The better to understand the cause of this double mo-tion ; let a resisting veflel, in which powder takes fire, be sup-posed to have the vent stopped at the beginning of the in-flammation, no motion will in this cafe be perceived, becausethe elastic fluid, pressing equally upon the fides of the con-taining vessel, and all the parts having a mutual attraction,its powers are in equilibrio : the balloon inflated with air isa very simple demonstration of this.

96. But if the elastic fluid can escape through an aperturemade on purpose, or through a cleft caused by its action onthe sides of the veflel, it will be impelled in a direction op-posite to the aperture, with a force proportionate to the den-sity and velocity of the fluid. For the elastic fluid inescaping meets resistance from the external air, and impelsit and the vessel in opposite directions ; and if the veflel itselfbe not equal in weight to the action of the fluid, it will beput in motion: since the column of air which resists thismotion, and tends to preserve the veflel in a state of rest, willnot be able to prevent it; (its resistance being proportional tothe velocity of bodies moving in it:) the greater the velocitywith which the fluid rushes out, the greater will be the re-sistance, and the longer the recoil: a number of experiments

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