kind of energy that sends the
projectile on its way.

In the dawn of history, war engines were performing the function of
artillery (which may be loosely defined as a means of hurling missiles
too heavy to be thrown by hand), and with these crude weapons the
basic principles of artillery were laid down. The Scriptures record
the use of ingenious machines on the walls of Jerusalem eight
centuries B.C.--machines that were probably predecessors of the
catapult and ballista, getting power from twisted ropes made of hair,
hide or sinew. The ballista had horizontal arms like a bow. The arms
were set in rope; a cord, fastened to the arms like a bowstring, fired
arrows, darts, and stones. Like a modern field gun, the ballista shot
low and directly toward the enemy.

The catapult was the howitzer, or mortar, of its day and could throw
a hundred-pound stone 600 yards in a high arc to strike the enemy
behind his wall or batter down his defenses. "In the middle of the
ropes a wooden arm rises like a chariot pole," wrote the historian
Marcellinus. "At the top of the arm hangs a sling. When battle is
commenced, a round stone is set in the sling. Four soldiers on each
side of the engine wind the arm down until it is almost level with the
ground. When the arm is set free, it springs up and hurls the stone
forth from its sling." In early times the weapon was called a
"scorpion," for like this dreaded insect it bore its "sting" erect.

[Illustration: Figure 1--BALLISTA. Caesar covered his landing in
Britain with fire from catapults and ballistas.]

The trebuchet was another war machine used extensively during the
Middle Ages. Essentially, it was a seesaw. Weights on the short arm
swung the long throwing arm.

[Illustration: Figure 2--CATAPULT.]

[Illustration: Figure 3--TREBUCHET. A heavy trebuchet could throw a
300-pound stone 300 yards.]

These weapons could be used with telling effect, as the Romans learned
from Archimedes in the siege of Syracuse (214-212 B.C.). As Plutarch
relates, "Archimedes soon began to play his engines upon the Romans
and their ships, and shot stones of such an enormous size and with so
incredible a noise and velocity that nothing could stand before them.
At length the Romans were so terrified that, if they saw but a rope
or a beam projecting over the walls of Syracuse, they cried out that
Archimedes was leveling some machine at them, and turned their backs
and fled."

Long after the introduction of