In its anterior portion was
a cylinder, furnished with cables, which held back a great beam bearing
a spoon for the reception of projectiles; its base was caught in a
skein of twisted thread, and when the ropes were let go it sprang up and
struck against the bar, which, checking it with a shock, multiplied its
power.
The second presented a more complicated mechanism. A cross-bar had its
centre fixed on a little pillar, and from this point of junction there
branched off at right angles a short of channel; two caps containing
twists of horse-hair stood at the extremities of the cross-bar; two
small beams were fastened to them to hold the extremities of a rope
which was brought to the bottom of the channel upon a tablet of bronze.
This metal plate was released by a spring, and sliding in grooves
impelled the arrows.
The catapults were likewise called onagers, after the wild asses which
fling up stones with their feet, and the ballistas scorpions, on account
of a hook which stood upon the tablet, and being lowered by a blow of
the fist, released the spring.
Their construction required learned calculations; the wood selected had
to be of the hardest substance, and their gearing all of brass; they
were stretched with levers, tackle-blocks, capstans or tympanums; the
direction of the shooting was changed by means of strong pivots; they
were moved forward on cylinders, and the most considerable of them,
which were brought piece by piece, were set up in front of the enemy.
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