A military dictionary

by William Duane

the lower part of any port where ordnance is planted. It likewise means that beam in a pontoon which supports the main waste.

GUNNER, in the artillery, is the title of the first and second artillerist at a gun in battery; all the rest are called aids.

GUNNERY, the art of determining the motions of bodies shot from cannon, mortars, howitzers, &c. See the article [Projectile].

The late ingenious Mr. Robins, having concluded from experiments, that the force of fired gunpowder, at the instant of its explosion, is the same with that of an elastic fluid of a thousand times the density of common air, and that the elasticity of this fluid, like that of the air, is proportional to its density, proposes the following problem.

The dimensions of any piece of artillery, the weight of its ball, and the quantity of its charge being given; to determine the velocity which the shot will acquire from the explosion, supposing the elasticity or force of the powder at the first instant of its firing to be given.

In the solution of this important problem, he assumes the two following principles: 1. That the action of the powder on the shot ceases as soon as it is got out of the piece. 2. That all the powder of the charge is fired, and converted into an elastic fluid, before the shot is sensibly moved from its place.

These assumptions, and the conclusions above mentioned, make the action of fired gunpowder to be entirely similar to that of air condensed a thousand times; and from thence it will not be difficult to determine the velocity of the shot arising from the explosion: for the force of the fired powder diminishing in proportion to its expansion, and ceasing when it is got out of the piece; the total action of the powder may be represented by the area of a curve, the base of which represents the space through which the ball is accelerated, while the ordinates represent the force of the powder at every point of that space; and these ordinates being in reciprocal proportion to their distance from the breech of the gun, because when the spaces occupied by the fired powder are as 1, 2, 3, 4, &c. the ordinates representing it will be as 1, 1-half, ¹⁄₃d, ¹⁄₄th, &c. It appears that the curve will be a common parabola, and that the area intercepted between is an asymptote; and that the two ordinates representing the force of the powder at the first explosion, and at the muzzle of the piece, will represent the total action of the powder on the shot; but if the shot were urged through the same space by an uniform force equal to its gravity, the total action of this force would be represented by a rectangle, the base of which would be the base of the curve or intercepted portion of the asymptote above mentioned, and the height of which would represent the uniform force of gravity. Hence the square of the velocity of the shot resulting from gravity is given, being the velocity it would acquire from a height equal to the space through which the powder accelerates it; and the proportion between the hyperbola and the rectangle is given from the analogy between the hyperbolic paces and logarithms; therefore the velocity of the ball arising from the action of the fired gunpowder will be given.

Mr. Robins has also given us an ingenious way of determining, by experiments, the velocity with which any shot moves at any distance of the piece it is discharged from.

This may be effected by means of a pendulum made of iron, having a broad part at bottom, covered with a thick piece of wood, which is fastened to the iron by screws; then having a machine like a common artillery-gin, on two of its poles, towards their tops, are screwed sockets, on which the pendulum is hung by means of a cross piece, which becomes its axis of suspension, and on which it should vibrate with great freedom. Somewhat lower than the bottom of the pendulum there should be a brace, joining to which the pendulum is suspended; and to this brace there is fastened a contrivance made with two edges of steel, something in the manner of a drawing-pen; the strength with which these edges press on each other, being diminished or increased at pleasure by means of a screw. To the bottom of the pendulum should be fastened a narrow riband, which, passing between the steel edges, may hang closely down by means of an opening cut in the lower piece of steel.

The instrument being thus fitted, if the weight of the pendulum, the respective distances of its centre of gravity, and of its centre of oscillation from the axis of suspension, be known, it may from thence be found what motion will be communicated to this pendulum by the percussion of a body of a known weight, moving with a known degree of velocity, and sinking it into a given point; that is, if the pendulum be supposed to rest before the percussion, it will be known what vibration it should make in consequence of such a blow; and if the pendulum, being at rest, is struck by a body of a known weight, and the vibration which the pendulum makes after the stroke is known, the velocity of the striking body may from thence be determined.