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1 Hero of Alexandria
SUBJECT AREA: Architecture and building, Mechanical, pneumatic and hydraulic engineering, Photography, film and optics, Steam and internal combustion engines[br]fl. c.62 AD Alexandria[br]Alexandrian mathematician and mechanician.[br]Nothing is known of Hero, or Heron, apart from what can be gleaned from the books he wrote. Their scope and style suggest that he was a teacher at the museum or the university of Alexandria, writing textbooks for his students. The longest book, and the one with the greatest technological interest, is Pneumatics. Some of its material is derived from the works of the earlier writers Ctesibius of Alexandria and Philo of Byzantium, but many of the devices described were invented by Hero himself. The introduction recognizes that the air is a body and demonstrates the effects of air pressure, as when air must be allowed to escape from a closed vessel before water can enter. There follow clear descriptions of a variety of mechanical contrivances depending on the effects of either air pressure or heated gases. Most of the devices seem trivial, but such toys or gadgets were popular at the time and Hero is concerned to show how they work. Inventions with a more serious purpose are a fire pump and a water organ. One celebrated gadget is a sphere that is set spinning by jets of steam—an early illustration of the reaction principle on which modern jet propulsion depends.M echanics, known only in an Arabic version, is a textbook expounding the theory and practical skills required by the architect. It deals with a variety of questions of mechanics, such as the statics of a horizontal beam resting on vertical posts, the theory of the centre of gravity and equilibrium, largely derived from Archimedes, and the five ways of applying a relatively small force to exert a much larger one: the lever, winch, pulley, wedge and screw. Practical devices described include sledges for transporting heavy loads, cranes and a screw cutter.Hero's Dioptra describes instruments used in surveying, together with an odometer or device to indicate the distance travelled by a wheeled vehicle. Catoptrics, known only in Latin, deals with the principles of mirrors, plane and curved, enunciating that the angle of incidence is equal to that of reflection. Automata describes two forms of puppet theatre, operated by strings and drums driven by a falling lead weight attached to a rope wound round an axle. Hero's mathematical work lies in the tradition of practical mathematics stretching from the Babylonians through Islam to Renaissance Europe. It is seen most clearly in his Metrica, a treatise on mensuration.Of all his works, Pneumatics was the best known and most influential. It was one of the works of Greek science and technology assimilated by the Arabs, notably Banu Musa ibn Shakir, and was transmitted to medieval Western Europe.[br]BibliographyAll Hero's works have been printed with a German translation in Heronis Alexandrini opera quae supersunt omnia, 1899–1914, 5 vols, Leipzig. The book on pneumatics has been published as The Pneumatics of Hero of Alexandria, 1851, trans. and ed. Bennet Wood-croft, London (facs. repr. 1971, introd. Marie Boas Hall, London and New York).Further ReadingA.G.Drachmann, 1948, "Ktesibios, Philon and Heron: A Study in Ancient Pneumatics", Acta Hist. Sci. Nat. Med. 4, Copenhagen: Munksgaard.T.L.Heath, 1921, A History of Greek Mathematics, Oxford (still useful for his mathematical work).LRD -
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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