1 The Birth of Science - MSRI

4.6 Hydraulic and Pneumatic Engineering 105
A very important technology, involving both hydraulic and mechanical
engineering, is water lifting. 89
The oldest machine for lifting water, the shaduf, is documented in Mesopotamia
around 2300 B.C. and in Egypt around 1600 B.C., and is still used
in many oriental cultures. It consists of a bucket at the end of a rod. The
rod pivots about its middle, at a height of some five feet, and the other end
has a clay block that serves as a counterweight. When the bucket is lifted
to a certain height, the contents can be poured into a runoff channel.
In the Hellenistic period water lifting technology was revolutionized
by the appearance of completely new devices, all of which date from no
earlier than the third and no later than the second century B.C. The field
witnessed no further progress in ancient times.
With the new machines, not only could much more water be lifted, but
most importantly, unlike the shaduf (which had to be operated with some
skill by a human), the necessary action can be “automated”, being reduced
to a continuous rotational motion that can be supplied by an animal or a
natural energy source. The simplest device of this type is the tympanum or page 145
waterwheel described by Vitruvius. 90 It is a hollow cylinder divided radially
into wedges (usually eight) which turns around a horizontal axis, the
lowest part being immersed in the water that must be lifted; the openings
are so placed that each wedge lets water in when it’s submerged and lets
it out when it rises above the axis. There is one defect: the water cannot
be raised a height greater than the radius of the tympanum. To lift the water
more one would use chains of buckets that were filled and emptied
automatically. The buckets could be attached to the edge of a wheel (so
the height of lifting would be the diameter of the wheel), of, if a greater
height was needed, the buckets could be attached to a chain connecting
two wheels, one placed at the departure level of the water and one at
the delivery level. As in the case of the tympanum, the raised water was
poured into a runoff channel. 91
The preceding machines have vertical wheels revolving around a horizontal
axis. But for using animal power it is much easier to rotate a horizontal
wheel about a vertical axis. Hellenistic gears allowed a solution to
the problem, leading to a device now called the sakiyeh (by the Arabs, who
still use it).
89
For a complete and up-to-date survey of the field, see [Oleson: WL].
90
Vitruvius, De architectura, X, iv, 1–2. The same wheel is cited in Chapter 61 of the Arabic version
of Philo of Byzantium’s Pneumatica.
91
The bucket chain is described in the (certainly corrupt) Arabic text of Chapter 65 of Philo of
Byzantium’s Pneumatica. Remains of a water-lifting system of this type, dating from the second
century B.C., have been found in Cosa in central Italy; see [Oleson: WL], pp. 258–261.
Revision: 1.14 Date: 2002/10/24 04:25:47