The Ctesibius clock was powered by water falling from a full tank through a pipe to an open cylinder. The cylinder had a floating piston with a rack that moved a pinion with a hand-shaped indicator that turned and pointed to the hour signs.
Ctesibius’s main improvement over previous water clocks was his adaptation to Egyptian hours, which were of a different duration according to whether it was day or night. This adaptation was achieved by a cone-shaped device to limit the flow to the cylinder, together with a pipe for discarding excess water. The disadvantage of the system was that the clock needed two manual adjustments every day, namely one in the morning and one in the evening.
Although both Egyptian day and night had 12 hours each (see picture above), the duration of a day-hour was different from a night-hour. It would be interesting to discuss with students why Egyptians used a time system so different from ours.
tags: invention, problem, discussion, innovation