Ctesibius Of Alexandria, Ctesibius also spelled Ktesibios, (flourished c. 270 BC), Greek physicist and inventor, the first great figure of the ancient engineering tradition of Alexandria, Egypt.
Ctesibius was the son of a barber. The discovery of the elasticity of air is attributed to Ctesibius, as is the invention of several devices using compressed air, including force pumps and an air-powered catapult. His most famous invention, however, was an improvement of the clepsydra, or water clock, in which water dripping at a constant rate raised a float that held a pointer to mark the passage of the hours. Another notable invention was a hydraulis, or water organ, in which air was forced through the organ pipes by the weight of water rather than by falling lead weights. Ctesibius’ writings have not survived, and his inventions are known only from references to them by Vitruvius and Hero of Alexandria, but he laid the foundations for the engineering tradition that culminated in the works of Hero of Alexandria and of Philo of Byzantium.
He was probably the first head of the Museum at Alexandria, invented the first artificial automatic self-regulatory system by designing an improved water clock or clepsydra (water thief) that required no outside intervention between the feedback and the controls of the mechanism. Ctesbius’s clepsydra kept more accurate time than any clock invented until the Dutch physicist Christiaan Huygens invented the pendulum clock, and studied the use of a pendulum to regulate a clock in the 17th century.
“During the first Alexandrian period, it [Ctesibius’s clock] was adapted as a way for physicians to count the pulse. It was also used in law courts to time speeches. A long tube was plunged into the water and when it was full, the opening at the top was closed. When it was reopened, the water dripped through a small opening at the lower end. A person was free to speak until the tube was empty. Theoretically, the interval between drips marked a specified time; however, the rate of flow increased when there was more water in the trube. As it emptied, the decrease in pressure slowed the dripping. Ctesbius’ objective was to regulate the clock so that the water level did not have to be continually tended. He used a three-tier system in which a large body of water emptied into the clepsydra to insure it remained full. A float and pointer set in a third container indicated the time elapsed. Ctesibus’ clepsydra remained the most accurate clock until the fourteenth century when mechanical clocks using a system of leaded weights and levers replaced hydraulic ones. The float in the clepsydra represents an early example of a feedback mechanism” (Nocks, The Robot. The Life Story of a Technology  12-13).
(Hydraulis, earliest known mechanical pipe organ. It was invented in the 3rd century BC by Ctesibius of Alexandria, culminating prior attempts to apply a mechanical wind supply to a large set of panpipes. Its pipes stood on top of a wind chest that was connected to a conical wind reservoir. The reservoir was supplied with air by one or two pumps. For the pipes to sound evenly, the wind chest needed steady air pressure. The open bottom of the cone was set in a tall outer container half filled with water. When air pressure in the cone was low, the water level rose inside it, compressing the air and restoring the former air pressure. The player operated keys or, on some instruments, sliders that let air into the pipes.
The hydraulis was used at outdoor public entertainments; its sound was loud and penetrating. Its use declined in the West by the 5th century AD, although Arab writers of the 9th century refer to it. Later medieval writers thought the hydraulis was a steam-whistle organ such as the calliope.
Clepsydra, also called water clock, ancient device for measuring time by the gradual flow of water. One form, used by the North American Indians and some African peoples, consisted of a small boat or floating vessel that shipped water through a hole until it sank. In another form, the vessel was filled with water that was allowed to escape through a hole, and the time was read from graduated lines on the interior measuring the level of the remaining water. It may have been an invention of the Chaldeans of ancient Babylonia; specimens from Egypt date from the 14th century BC. The Romans invented a clepsydra consisting of a cylinder into which water dripped from a reservoir; a float provided readings against a scale on the cylinder wall. Clepsydras were used for many purposes, including timing the speeches of orators; as late as the 16th century, Galileo used a mercury clepsydra to time his experimental falling bodies.)
It seems his first invention was a counter-weighted mirror and was made during his barber period. In the barbershop he constructed an automation—a mirror, fixed on one end of a pole and a lead weight, weighing the same as the mirror, was on the other. This acted as a counterbalance and enabled the mirror, using some system of rods, to adjust to the height of different customers. Ctesibius had the lead counter-balance weight running inside a tube and noticed that as the counterweight moved rapidly through the tube, the compressed trapped air which escaped with a loud noise. This effect provoked his curiosity about both the powers of air, and musical instruments, e.g. water organ, and will result in his famous Pneumatica.
Some historians suppose Ctesibius was a favorite of the king of Egypt Ptolemy II (also known as Ptolemy II Philadelphus, who ruled from 283 BC to 246 BC), who supported the inventor, while others claim all his life was miserably poor. Ctesibius is said to have married to a woman named Thais.
In addition to inventing the water organ (hydraulis) and suction pump, Ctesibius also perfected the first accurate water clock (see the upper image). Previous water clocks did not keep precise time because the flow of water to the clock could not be correctly regulated. Ctesibius first fashioned orifices of gold or other substances which would not be worn by the action of water and did not collect dirt. Having guaranteed an uninterrupted water flow into the first chamber of the clock, Ctesibius then devised a way to keep the water level in that chamber constant. An automatic valve, worked by a float, shut off the supply when the water in the chamber rose too high and opened it again as soon as enough water had drained into the clock’s second chamber. The flow of water from the first chamber to the second, consequently, was always the same, and the passage of a certain amount of water represented the passage of so much time. On the simplest of water clocks, elapsed time could be determined by noting the markings on the side of the second chamber. More elaborate water clocks had complex and imaginative ways of denoting the time.
Ctesibius is known also for several other discoveries, e.g. cannons operated by compressed air and a hydraulic hoist, capable of raising very heavy weights.
Ctesibius is also credited with a considerable number of automatic devices, designed for entertainment. These included:
1. A singing cornucopia, incorporated into the funeral monument erected by Ptolemy in honor of his wife and sister Arsinoë in 270 BC.
2. A cam-operated statue of the mysterious deity that figured prominently in the famous Grand Procession, where it carried out a continuous performance, entertaining the festival crowd by standing up and sitting down. The excitement produced by this very simple application of a rack-and-pinion gear may well be due to the fact that toothed gear wheels were a recent invention, which almost certainly meant that their possibilities were still being explored (there is a passage in the Aristotle’s Problemata (a multifaceted text asking various questions about medical, scientific or everyday topics), in which Aristotle finds the reverse motion created by two intersecting cogwheels intriguing).
Ctesibius is considered the founder of the Alexandrian school of mathematics and engineering, and was probably the first head of the Museum of Alexandria.
(Sources: https://www.britannica.com/biography/Ctesibius-of-Alexandria, https://www.britannica.com/art/hydraulis, http://www.historyofinformation.com/expanded.php?id=2306, http://history-computer.com/Dreamers/Ctesibius.html, https://www.britannica.com/technology/clepsydra)
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