Most technical phrases are explained in the text and illustrations
(see fig. 51). For convenient reference, however, some important words
are defined below:
*Ballistics*--the science dealing with the motion of projectiles.
*Barbette carriage*--as used here, a traverse carriage on which a gun
is mounted to fire over a parapet.
*Bomb, bombshell*--see projectiles.
Breechblock--a movable piece which closes the breech of a cannon.
*Caliber*--diameter of the bore; also used to express bore length. A
30-caliber gun has a bore length 30 times the diameter of the bore.
*Cartridge*--a bag or case holding a complete powder charge for the
cannon, and in some instances also containing the projectile.
*Casemate carriage*--as used here, a traverse carriage in a fort
gunroom (casemate). The gun fired through an embrasure or loophole in
the wall of the room.
*Chamber*--the part of the bore which holds the propelling charge,
especially when of different diameter than the rest of the bore; in
chambered muzzle-loaders, the chamber diameter was smaller than that
of the bore.
*Elevation*--the angle between the axis of a piece and the horizontal
plane.
*Fuze*--a device to ignite the charge of a shell or other projectile.
*Grommet*--a rope ring used as a wad to hold a cannonball in place in
the bore.
*Gun*--any firearm; in the limited sense, a long cannon with high
muzzle velocity and flat trajectory.
*Howitzer*--a short cannon, intermediate between the gun and mortar.
*Lay*--to aim a gun.
*Limber*--a two-wheeled vehicle to which the gun trail is attached for
transport.
*Mandrel*--a metal bar, used as a core around which metal may be
forged or otherwise shaped.
*Mortar*--a very short cannon used for high or curved trajectory
firing.
*Point-blank*--as used here, the point where the projectile, when
fired from a level bore, first strikes the horizontal ground in front
of the cannon.
*Projectiles*--_canister or case shot_: a can filled with small
missiles that scatter after firing from the gun. _Grape shot_: a
cluster of small iron balls, which scatter upon firing. _Shell_:
explosive missile; a hollow cast-iron ball, filled with gunpowder,
with a fuze to produce detonation; a long, hollow projectile, filled
with explosive and fitted with a fuze. _Shot_: a solid projectile,
non-explosive.
*Quoin*--a wedge placed under the breech of a gun to fix its
elevation.
*Range*--The horizontal distance from a gun to its target or to the
point where the projectile first strikes the ground. _Effective range_
is the distance at which effective results may be expected, and is
usually not the same as _maximum range_, which means the extreme limit
of range.
*Rotating band*--a band of soft metal, such as copper, which encircles
the projectile near its base. By engaging the lands of the spiral
rifling in the bore, the band causes rotation of the projectile.
Rotating bands for muzzle-loading cannon were expansion rings, and the
powder blast expanded the ring into the rifling grooves.
*Train*--to aim a gun.
*Trajectory*--curved path taken by a projectile in its flight through
the air.
*Transom*--horizontal beam between the cheeks of a gun carriage.
*Traverse carriage*--as used here, a stationary gun mount, consisting
of a gun carriage on a wheeled platform which can be moved about a
pivot for aiming the gun to right or left.
*Windage*--as used here, the difference between the diameter of the
shot and the diameter of the bore.
[Illustration: Figure 51--THE PARTS OF A CANNON.]