Ctesibius of Alexandria

300?-200? b.c.

Greek Physicist and Inventor

Ctesibius (also spelled Ktesibios) was a Greek physicist and inventor who was probably born in Alexandria sometime around 300 b.c.. He was the first of many Greeks to become part of the great ancient engineering tradition in Alexandria, Egypt, and, as such, was the influential predecessor to many subsequent inventors. While he was an enthusiastic and prolific inventor, he is most famous for two particular inventions. The first was an improvement of the clepsydra or water clock, by which time was kept with dripping water maintained at a constant rate. The second invention was the hydraulis or water organ, a mechanized device in which air was forced by water through organ pipes to produce sounds.

Like many of the significant individuals from antiquity, very little is known about the life of Ctesibius. There are no direct sources dealing with his life and times, but a cloudy sketch of his life can be pieced together from various historians. Ctesibius was born the son of a barber and started out in the same career. One of his first inventions was an occupationally related counterweighted mirror.

The device involved a mirror, placed at the end of a tubular pole, and a lead counterweight of the exact same weight, placed at the other end. This setup would allow the mirror to be adjusted readily to accommodate the height of each patron. Ctesibius also noticed that when he moved the mirror, the weight bounced up and down while making a strange whistling noise. He understood this noise to be the air escaping from the tube and wondered if this principle could be utilized to make music. He began to think about the power of both air and water and made use of them in his inventions.

Ctesibius has been credited with building singing statues, pumps, water clocks, and the world's first keyboard instrument. His improvement of the water clock resulted in a time-recording device whose accuracy would not be surpassed for over 1,500 years.

Modern society is to a large extent dictated by time. We need and rely on accurate devices to measure the passage of time. This, however, is a relatively recent phenomenon. In the past, the forces of nature, rather than raw time, governed people's lives. In addition, the technology needed to measure accurate time was not well understood. During Ctesibius's day, water clocks were used to measure the time that defendants were able to speak when on trial. It was a simple device much like an hourglass, but with water rather than sand as the timekeeping medium. Water was placed into a jar with hole in the bottom, and when the water ran out, so did the defendant's time. Ctesibius realized that as the volume of water changed, so did the time, so he improved on the design by adding two other containers. The first feed into the jar to keep it at a constant level and the second had a float with a pointer that could accurately measure the number of drips. In this fashion, Ctesibius invented a timing device that remained the primary model until into the fourteenth century, when falling weights replaced falling water.

Ctesibius has also been credited with the invention of the organ. He recognized that water displaced air in a bucket and used that principle to keep the pressure high in the organ even when the pump was on the recovery cycle. This gave his organ a continuous sound, which could be changed by selecting different operating valves. It is unfortunate that our knowledge of Ctesibius is severely fragmented and secondhand. He was obviously a mechanical genius who influenced his peers and certainly left a much greater legacy than he is given credit for.

JAMES J. HOFFMANN