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.