The Ten Books on Architecture
of the poles, so that, by distributing the dead weight of the burden
according to a definitely proportioned division, each labourer may have
an equal share to carry on his neck. For the poles, from which the
straps for the burden of the four porters hang, are marked off at their
centres by nails, to prevent the straps from slipping to one side. If
they shift beyond the mark at the centre, they weigh heavily upon the
place to which they have come nearer, like the weight of a steelyard
when it moves from the point of equilibrium towards the end of the
weighing apparatus.
8. In the same way, oxen have an equal draught when their yoke is
adjusted at its middle by the yokestrap to the pole. But when their
strength is not the same, and the stronger outdoes the other, the strap
is shifted so as to make one side of the yoke longer, which helps the
weaker ox. Thus, in the case of both poles and yokes, when the straps
are not fastened at the middle, but at one side, the farther the strap
moves from the middle, the shorter it makes one side, and the longer the
other. So, if both ends are carried round in circles, using as a centre
the point to which the strap has been brought, the longer end will
describe a larger, and the shorter end a smaller circle.
9. Just as smaller wheels move harder and with greater difficulty than
larger ones, so, in the case of the poles and yokes, the parts where the
interval from centre to end is less, bear down hard upon the neck, but
where the distance from the same centre is greater, they ease the burden
both for draught and carriage. As in all these cases motion is obtained
by means of right lines at the centre and by circles, so also farm
waggons, travelling carriages, drums, mills, screws, scorpiones,
ballistae, pressbeams, and all other machines, produce the results
intended, on the same principles, by turning about a rectilinear axis
and by the revolution of a circle.
CHAPTER IV
ENGINES FOR RAISING WATER
1. I shall now explain the making of the different kinds of engines
which have been invented for raising water, and will first speak of the
tympanum. Although it does not lift the water high, it raises a great
quantity very quickly. An axle is fashioned on a lathe or with the
compasses, its ends are shod with iron hoops, and it carries round its
middle a tympanum made of boards joined together. It rests on posts
which have pieces of iron on them under the ends of the axle. In the
interior of this tympanum there are eight crosspieces set at intervals,
extending from the axle to the circumference of the tympanum, and
dividing the space in the tympanum into equal compartments.
2. Planks are nailed round the face of it, leaving six-inch apertures to
admit the water. At one side of it there are also holes, like those of a
dovecot, next to the axle, one for each compartment. After being smeared
with pitch like a ship, the thing is turned by the tread of men, and
raising the water by means of the apertures in the face of the tympanum,
delivers it through the holes next to the axle into a wooden trough set
underneath, with a conduit joined to it. Thus, a large quantity of water
is furnished for irrigation in gardens, or for supplying the needs of
saltworks.
3. But when it has to be raised higher, the same principle will be
modified as follows. A wheel on an axle is to be made, large enough to
reach the necessary height. All round the circumference of the wheel
there will be cubical boxes, made tight with pitch and wax. So, when the
wheel is turned by treading, the boxes, carried up full and again
returning to the bottom, will of themselves discharge into the reservoir
what they have carried up.
4. But, if it has to be supplied to a place still more high, a double
iron chain, which will reach the surface when let down, is passed round
the axle of the same wheel, with bronze buckets attached to it, each
holding about six pints. The turning of the wheel, winding the chain
round the axle, will carry the buckets to the top, and as they pass
above the axle they must tip over and deliver into the reservoir what
they have carried up.
CHAPTER V
WATER WHEELS AND WATER MILLS
1. Wheels on the principles that have been described above are also
constructed in rivers. Round their faces floatboards are fixed, which,
on being struck by the current of the river, make the wheel turn as they
move, and thus, by raising the water in the boxes and bringing it to the
top, they accomplish the necessary work through being turned by the mere
impulse of the river, without any treading on the part of workmen.
2. Water mills are turned on the same principle. Everything is the same
in them, except that a drum with teeth is fixed into one end of the
axle. It is set vertically on its edge, and turns in the same plane with
the wheel. Next to this larger drum there is a smaller one, also with
teeth, but set horizontally, and this is attached (to the millstone).
Thus the teeth of the drum which is fixed to the axle make the teeth of
the horizontal drum move, and cause the mill to turn. A hopper, hanging
over this contrivance, supplies the mill with corn, and meal is produced
by the same revolution.
CHAPTER VI
THE WATER SCREW
1. There is also the method of the screw, which raises a great quantity
of water, but does not carry it as high as does the wheel. The method of
constructing it is as follows. A beam is selected, the thickness of
which in digits is equivalent to its length in feet. This is made
perfectly round. The ends are to be divided off on their circumference
with the compass into eight parts, by quadrants and octants, and let the
lines be so placed that, if the beam is laid in a horizontal position,
the lines on the two ends may perfectly correspond with each other, and
intervals of the size of one eighth part of the circumference of the
beam may be laid off on the length of it. Then, placing the beam in a
horizontal position, let perfectly straight lines be drawn from one end
to the other. So the intervals will be equal in the directions both of
the periphery and of the length. Where the lines are drawn along the
length, the cutting circles will make intersections, and definite points
at the intersections.
2. When these lines have been correctly drawn, a slender withe of
willow, or a straight piece cut from the agnus castus tree, is taken,
smeared with liquid pitch, and fastened at the first point of
intersection. Then it is carried across obliquely to the succeeding
intersections of longitudinal lines and circles, and as it advances,
passing each of the points in due order and winding round, it is
fastened at each intersection; and so, withdrawing from the first to the
eighth point, it reaches and is fastened to the line to which its first
part was fastened. Thus, it makes as much progress in its longitudinal
advance to the eighth point as in its oblique advance over eight
points. In the same manner, withes for the eight divisions of the
diameter, fastened obliquely at the intersections on the entire
longitudinal and peripheral surface, make spiral channels which
naturally look just like those of a snail shell.
3. Other withes are fastened on the line of the first, and on these
still others, all smeared with liquid pitch, and built up until the
total diameter is equal to one eighth of the length. These are covered
and surrounded with boards, fastened on to protect the spiral. Then
these boards are soaked with pitch, and bound together with strips of
iron, so that they may not be separated by the pressure of the water.
The ends of the shaft are covered with iron. To the right and left of
the screw are beams, with crosspieces fastening them together at both
ends. In these crosspieces are holes sheathed with iron, and into them
pivots are introduced, and thus the screw is turned by the treading of
men.
4. It is to be set up at an inclination corresponding to that which is
produced in drawing the Pythagorean right-angled triangle: that is, let
its length be divided into five parts; let three of them denote the
height of the head of the screw; thus the distance from the base of the
perpendicular to the nozzle of the screw at the bottom will be equal to
four of those parts. A figure showing how this ought to be, has been
drawn at the end of the book, right on the back.
I have now described as clearly as I could, to make them better known,
the principles on which wooden engines for raising water are
constructed, and how they get their motion so that they may be of
unlimited usefulness through their revolutions.
CHAPTER VII
THE PUMP OF CTESIBIUS
1. Next I must tell about the machine of Ctesibius, which raises water
to a height. It is made of bronze, and has at the bottom a pair of
cylinders set a little way apart, and there is a pipe connected with
each, the two running up, like the prongs of a fork, side by side to a
vessel which is between the cylinders. In this vessel are valves,
accurately fitting over the upper vents of the pipes, which stop up the
ventholes, and keep what has been forced by pressure into the vessel
from going down again.
2. Over the vessel a cowl is adjusted, like an inverted funnel, and
fastened to the vessel by means of a wedge thrust through a staple, to
prevent it from being lifted off by the pressure of the water that is
forced in. On top of this a pipe is jointed, called the trumpet, which
stands up vertically. Valves are inserted in the cylinders, beneath the
lower vents of the pipes, and over the openings which are in the bottoms
of the cylinders.
3. Pistons smoothly turned, rubbed with oil, and inserted from above
into the cylinders, work with their rods and levers upon the air and
water in the cylinders, and, as the valves stop up the openings, force
and drive the water, by repeated pressure and expansion, through the
vents of the pipes into the vessel, from which the cowl receives the
inflated currents, and sends them up through the pipe at the top; and so
water can be supplied for a fountain from a reservoir at a lower level.
4. This, however, is not the only apparatus which Ctesibius is said to
have thought out, but many more of various kinds are shown by him to
produce effects, borrowed from nature, by means of water pressure and
compression of the air; as, for example, blackbirds singing by means of
waterworks, and "angobatae," and figures that drink and move, and other
things that are found to be pleasing to the eye and the ear.
5. Of these I have selected what I considered most useful and necessary,
and have thought it best to speak in the preceding book about
timepieces, and in this about the methods of raising water. The rest,
which are not subservient to our needs, but to pleasure and amusement,
may be found in the commentaries of Ctesibius himself by any who are
interested in such refinements.
CHAPTER VIII
THE WATER ORGAN
1. With regard to water organs, however, I shall not fail with all
possible brevity and precision to touch upon their principles, and to
give a sufficient description of them. A wooden base is constructed, and
on it is set an altar-shaped box made of bronze. Uprights, fastened
together like ladders, are set up on the base, to the right and to the
left (of the altar). They hold the bronze pump-cylinders, the moveable
bottoms of which, carefully turned on a lathe, have iron elbows fastened
to their centres and jointed to levers, and are wrapped in fleeces of
wool. In the tops of the cylinders are openings, each about three digits
in diameter. Close to these openings are bronze dolphins, mounted on