CATAPULTS OR SCORPIONES
1. I shall next explain the symmetrical principles on which scorpiones
and ballistae may be constructed, inventions devised for defence against
danger, and in the interest of self-preservation.
The proportions of these engines are all computed from the given length
of the arrow which the engine is intended to throw, and the size of the
holes in the capitals, through which the twisted sinews that hold the
arms are stretched, is one ninth of that length.
2. The height and breadth of the capital itself must then conform to the
size of the holes. The boards at the top and bottom of the capital,
which are called "peritreti," should be in thickness equal to one hole,
and in breadth to one and three quarters, except at their extremities,
where they equal one hole and a half. The sideposts on the right and
left should be four holes high, excluding the tenons, and five twelfths
of a hole thick; the tenons, half a hole. The distance from a sidepost
to the hole is one quarter of a hole, and it is also one quarter of a
hole from the hole to the post in the middle. The breadth of the post
in the middle is equal to one hole and one eighth, the thickness, to one
hole.
3. The opening in the middle post, where the arrow is laid, is equal to
one fourth of the hole. The four surrounding corners should have iron
plates nailed to their sides and faces, or should be studded with bronze
pins and nails. The pipe, called [Greek: syrigx] in Greek, has a length
of nineteen holes. The strips, which some term cheeks, nailed at the
right and left of the pipe, have a length of nineteen holes and a height
and thickness of one hole. Two other strips, enclosing the windlass, are
nailed on to these, three holes long and half a hole in breadth. The
cheek nailed on to them, named the "bench," or by some the "box," and
made fast by means of dove-tailed tenons, is one hole thick and seven
twelfths of a hole in height. The length of the windlass is equal
to...[12] holes, the thickness of the windlass to three quarters of a
hole.
[Note 12: The dots here and in what follows, indicate lacunae in
the manuscripts.]
4. The latch is seven twelfths of a hole in length and one quarter in
thickness. So also its socket-piece. The trigger or handle is three
holes in length and three quarters of a hole in breadth and thickness.
The trough in the pipe is sixteen holes in length, one quarter of a hole
in thickness, and three quarters in height. The base of the standard on
the ground is equal to eight holes; the breadth of the standard where it
is fastened into the plinth is three quarters of a hole, its thickness
two thirds of a hole; the height of the standard up to the tenon is
twelve holes, its breadth three quarters of a hole, and its thickness
two thirds. It has three struts, each nine holes in length, half a hole
in breadth, and five twelfths in thickness. The tenon is one hole in
length, and the head of the standard one hole and a half in length.
5. The antefix has the breadth of a hole and one eighth, and the
thickness of one hole. The smaller support, which is behind, termed in
Greek [Greek: antibasis], is eight holes long, three quarters of a hole
broad, and two thirds thick. Its prop is twelve holes long, and has the
same breadth and thickness as the smaller support just mentioned. Above
the smaller support is its socket-piece, or what is called the cushion,
two and a half holes long, one and a half high, and three quarters of a
hole broad. The windlass cup is two and seven twelfths holes long, two
thirds of a hole thick, and three quarters broad. The crosspieces with
their tenons have the length of... holes, the breadth of three quarters,
and the thickness of two thirds of a hole. The length of an arm is seven
holes, its thickness at its base two thirds of a hole, and at its end
one half a hole; its curvature is equal to two thirds of a hole.
6. These engines are constructed according to these proportions or with
additions or diminutions. For, if the height of the capitals is greater
than their width--when they are called "high-tensioned,"--something
should be taken from the arms, so that the more the tension is weakened
by height of the capitals, the more the strength of the blow is
increased by shortness of the arms. But if the capital is less
high,--when the term "low-tensioned" is used,--the arms, on account of
their strength, should be made a little longer, so that they may be
drawn easily. Just as it takes four men to raise a load with a lever
five feet long, and only two men to lift the same load with a ten-foot
lever, so the longer the arms, the easier they are to draw, and the
shorter, the harder.
I have now spoken of the principles applicable to the parts and
proportions of catapults.