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1 ancient roman catapult
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2 Ctesibius (Ktesibios) of Alexandria
[br]fl. c.270 BC Alexandria[br]Alexandrian mechanician and inventor.[br]Ctesibius made a number of inventions of great importance, which he described in his book Pneumatics, now lost. The Roman engineer and architect Vitruvius quoted extracts from Ctesibius' work in his De Architectura and tells us that Ctesibius was the son of a barber and that he arranged an adjustable mirror controlled by a lead counterweight descending in a cylinder. He noticed that the weight compressed the air, which could be released with a loud noise. That led him to realize that the air was a body or substance: by means of a cylinder and plunger, he went on to invent an air pump with valves. This he connected to the keyboard and rows of pipes of an organ. He also invented a force pump for water.Ctesibius also improved the clepsydra or water clock, which measured time by the fall of water level in a vessel as the water escaped through a hole in the bottom. The rate of flow varied as the level dropped, so Ctesibius interposed a cistern with an overflow pipe, enabling the water level to be maintained; there was thus a constant flow into a cylinder and the passage of time was indicated by a float with a pointer. He fitted a rack to the float which turned a toothed wheel, to activate bells, singing birds or other "toys". This is probably the first known use of toothed gearing.Ctesibius is credited with some other inventions of a military nature, such as a catapult, but it was his pumps that established a tradition in antiquity for mechanical invention using the pressure of the air and other fluids, stretching through Philo of Byzantium (c.150 BC) and Hero of Alexandria (c.62 AD) and on through Islam into medieval Western Europe.[br]Further ReadingA.G.Drachmann, 1948, Ktesibios, Philon and Heron: A Study in Ancient Pneumatics, Copenhagen: Munksgaard (Acta Hist. Sci. Nat. Med. 4).LRDBiographical history of technology > Ctesibius (Ktesibios) of Alexandria
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