Heronis Alexandrini opera quae supersunt omnia

SUBJECT AREA: Architecture and building, Mechanical, pneumatic and hydraulic engineering, Photography, film and optics, Steam and internal combustion engines

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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.

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