ALS AND WATER CLOCKS

1. The semicircular form, hollowed out of a square block, and cut under
to correspond to the polar altitude, is said to have been invented by
Berosus the Chaldean; the Scaphe or Hemisphere, by Aristarchus of Samos,
as well as the disc on a plane surface; the Arachne, by the astronomer
Eudoxus or, as some say, by Apollonius; the Plinthium or Lacunar, like
the one placed in the Circus Flaminius, by Scopinas of Syracuse; the
[Greek: pros ta historoumena], by Parmenio; the [Greek: pros pan klima],
by Theodosius and Andreas; the Pelecinum, by Patrocles; the Cone, by
Dionysodorus; the Quiver, by Apollonius. The men whose names are written
above, as well as many others, have invented and left us other kinds:
as, for instance, the Conarachne, the Conical Plinthium, and the
Antiborean. Many have also left us written directions for making dials
of these kinds for travellers, which can be hung up. Whoever wishes to
find their baseplates, can easily do so from the books of these writers,
provided only he understands the figure of the analemma.

2. Methods of making water clocks have been investigated by the same
writers, and first of all by Ctesibius the Alexandrian, who also
discovered the natural pressure of the air and pneumatic principles. It
is worth while for students to know how these discoveries came about.
Ctesibius, born at Alexandria, was the son of a barber. Preeminent for
natural ability and great industry, he is said to have amused himself
with ingenious devices. For example, wishing to hang a mirror in his
father's shop in such a way that, on being lowered and raised again, its
weight should be raised by means of a concealed cord, he employed the
following mechanical contrivance.

3. Under the roof-beam he fixed a wooden channel in which he arranged a
block of pulleys. He carried the cord along the channel to the corner,
where he set up some small piping. Into this a leaden ball, attached to
the cord, was made to descend. As the weight fell into the narrow limits
of the pipe, it naturally compressed the enclosed air, and, as its fall
was rapid, it forced the mass of compressed air through the outlet into
the open air, thus producing a distinct sound by the concussion.

4. Hence, Ctesibius, observing that sounds and tones were produced by
the contact between the free air and that which was forced from the
pipe, made use of this principle in the construction of the first water
organs. He also