plosive properties of picric acid were
discovered, and melanite, ballistite, and cordite appeared in the last
quarter of the century, so that by 1890 nitrocellulose and
nitroglycerin-base powders had generally replaced black powder as a
propellant.

Still, black powder had many important uses. Its sensitivity to flame,
high rate of combustion, and high temperature of explosion made it a
very suitable igniter or "booster," to insure the complete ignition of
the propellant. Further, it was the main element in such modern
projectile fuzes as the ring fuze of the U. S. Field Artillery, which
was long standard for bursts shorter than 25 seconds. This fuze was in
the nose of the shell and consisted essentially of a plunger, primer,
and rings grooved to hold a 9-inch train of compressed black powder.
To set the fuze, the fuze man merely turned a movable ring to the
proper time mark. Turning the zero mark toward the channel leading to
the shell's bursting charge shortened the burning distance of the
train, while turning zero away from the channel, of course, did the
opposite. When the projectile left the gun, the shock made the plunger
ignite the primer (compare fig. 42e) and fire the powder train, which
then burned for the set time before reaching the shell charge. It was
a technical improvement over the tubular sheet-iron fuze of the
Venetians, but the principle was about the same.

[Illustration: Figure 21--MODERN POWDER TRAIN FUZE.]

THE CHARACTERISTICS OF CANNON

THE EARLY SMOOTHBORE CANNON

Soon after he found he could hurl a rock with his good right arm, man
learned about trajectory--the curved path taken by a missile through
the air. A baseball describes a "flat" trajectory every time the
pitcher throws a hard, fast one. Youngsters tossing the ball to each
other over a tall fence use "curved" or "high" trajectory. In
artillery, where trajectory is equally important, there are three main
types of cannon: (1) the flat trajectory gun, throwing shot at the
target in relatively level flight; (2) the high trajectory mortar,
whose shell will clear high obstacles and descend upon the target from
above; and (3) the howitzer, an in-between piece of medium-high
trajectory, combining the mobility of the fieldpiece with the large
caliber of the mortar.

The Spaniard, Luis Collado, mathematician, historian, native of
Lebrija in Andalusia, and, in 1592, royal engineer of His Catholic
Majesty's Army in Lombardy and Pied