The Ten Books on Architecture
joints and holding chains in their mouths, from which hang cymbal-shaped
valves, let down under the openings in the cylinders.
2. Inside the altar, which holds the water, is a regulator shaped like
an inverted funnel, under which there are cubes, each about three digits
high, keeping a free space below between the lips of the regulator and
the bottom of the altar. Tightly fixed on the neck of the regulator is
the windchest, which supports the principal part of the contrivance,
called in Greek the [Greek: kanôn mousikos]. Running longitudinally,
there are four channels in it if it is a tetrachord; six, if it is a
hexachord; eight, if it is an octachord.
3. Each of the channels has a cock in it, furnished with an iron handle.
These handles, when turned, open ventholes from the windchest into the
channels. From the channels to the canon there are vertical openings
corresponding to ventholes in a board above, which board is termed
[Greek: pinax] in Greek. Between this board and the canon are inserted
sliders, pierced with holes to correspond, and rubbed with oil so that
they can be easily moved and slid back into place again. They close the
above-mentioned openings, and are called the plinths. Their going and
coming now closes and now opens the holes.
4. These sliders have iron jacks fixed to them, and connected with the
keys, and the keys, when touched, make the sliders move regularly. To
the upper surface of the openings in the board, where the wind finds
egress from the channels, rings are soldered, and into them the reeds of
all the organ pipes are inserted. From the cylinders there are
connecting pipes attached to the neck of the regulator, and directed
towards the ventholes in the windchest. In the pipes are valves, turned
on a lathe, and set (where the pipes are connected with the cylinders).
When the windchest has received the air, these valves will stop up the
openings, and prevent the wind from coming back again.
5. So, when the levers are raised, the elbows draw down the bottoms of
the cylinders as far as they can go; and the dolphins, which are mounted
on joints, let the cymbals fall into the cylinders, thus filling the
interiors with air. Then the elbows, raising the bottoms within the
cylinders by repeated and violent blows, and stopping the openings above
by means of the cymbals, compress the air which is enclosed in the
cylinders, and force it into the pipes, through which it runs into the
regulator, and through its neck into the windchest. With a stronger
motion of the levers, the air is still more compressed, streams through
the apertures of the cocks, and fills the channels with wind.
6. So, when the keys, touched by the hand, drive the sliders forward and
draw them back regularly, alternately stopping and opening the holes,
they produce resonant sounds in a great variety of melodies conforming
to the laws of music.
With my best efforts I have striven to set forth an obscure subject
clearly in writing, but the theory of it is not easy, nor readily
understood by all, save only those who have had some practice in things
of this kind. If anybody has failed to understand it, he will certainly
find, when he comes to know the thing itself, that it is carefully and
exquisitely contrived in all respects.
CHAPTER IX
THE HODOMETER
1. The drift of our treatise now turns to a useful invention of the
greatest ingenuity, transmitted by our predecessors, which enables us,
while sitting in a carriage on the road or sailing by sea, to know how
many miles of a journey we have accomplished. This will be possible as
follows. Let the wheels of the carriage be each four feet in diameter,
so that if a wheel has a mark made upon it, and begins to move forward
from that mark in making its revolution on the surface of the road, it
will have covered the definite distance of twelve and a half feet on
reaching that mark at which it began to revolve.
2. Having provided such wheels, let a drum with a single tooth
projecting beyond the face of its circumference be firmly fastened to
the inner side of the hub of the wheel. Then, above this, let a case be
firmly fastened to the body of the carriage, containing a revolving drum
set on edge and mounted on an axle; on the face of the drum there are
four hundred teeth, placed at equal intervals, and engaging the tooth of
the drum below. The upper drum has, moreover, one tooth fixed to its
side and standing out farther than the other teeth.
3. Then, above, let there be a horizontal drum, similarly toothed and
contained in another case, with its teeth engaging the tooth fixed to
the side of the second drum, and let as many holes be made in this
(third) drum as will correspond to the number of miles--more or less, it
does not matter--that a carriage can go in a day's journey. Let a small
round stone be placed in every one of these holes, and in the receptacle
or case containing that drum let one hole be made, with a small pipe
attached, through which, when they reach that point, the stones placed
in the drum may fall one by one into a bronze vessel set underneath in
the body, of the carriage.
4. Thus, as the wheel in going forward carries with it the lowest drum,
and as the tooth of this at every revolution strikes against the teeth
of the upper drum, and makes it move along, the result will be that the
upper drum is carried round once for every four hundred revolutions of
the lowest, and that the tooth fixed to its side pushes forward one
tooth of the horizontal drum. Since, therefore, with four hundred
revolutions of the lowest drum, the upper will revolve once, the
progress made will be a distance of five thousand feet or one mile.
Hence, every stone, making a ringing sound as it falls, will give
warning that we have gone one mile. The number of stones gathered from
beneath and counted, will show the number of miles in the day's journey.
5. On board ship, also, the same principles may be employed with a few
changes. An axle is passed through the sides of the ship, with its ends
projecting, and wheels are mounted on them, four feet in diameter, with
projecting floatboards fastened round their faces and striking the
water. The middle of the axle in the middle of the ship carries a drum
with one tooth projecting beyond its circumference. Here a case is
placed containing a drum with four hundred teeth at regular intervals,
engaging the tooth of the drum that is mounted on the axle, and having
also one other tooth fixed to its side and projecting beyond its
circumference.
6. Above, in another case fastened to the former, is a horizontal drum
toothed in the same way, and with its teeth engaging the tooth fixed to
the side of the drum that is set on edge, so that one of the teeth of
the horizontal drum is struck at each revolution of that tooth, and the
horizontal drum is thus made to revolve in a circle. Let holes be made
in the horizontal drum, in which holes small round stones are to be
placed. In the receptacle or case containing that drum, let one hole be
opened with a small pipe attached, through which a stone, as soon as the
obstruction is removed, falls with a ringing sound into a bronze vessel.
7. So, when a ship is making headway, whether under oars or under a gale
of wind, the floatboards on the wheels will strike against the water and
be driven violently back, thus turning the wheels; and they, revolving,
will move the axle, and the axle the drum, the tooth of which, as it
goes round, strikes one of the teeth of the second drum at each
revolution, and makes it turn a little. So, when the floatboards have
caused the wheels to revolve four hundred times, this drum, having
turned round once, will strike a tooth of the horizontal drum with the
tooth that is fixed to its side. Hence, every time the turning of the
horizontal drum brings a stone to a hole, it will let the stone out
through the pipe. Thus by the sound and the number, the length of the
voyage will be shown in miles.
I have described how to make things that may be provided for use and
amusement in times that are peaceful and without fear.
CHAPTER X
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