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# Hero of Alexandria (c.10–70 AD)

Hero of Alexandria was a Greek mathematician, scientist, and inventor who is mostly renowned for his works in mechanics, mathematics and physics. Although there were about 18 Greek writers under the name of Hero or Heron, this specific Greek scientist was known as Hero or Heron of Alexandria. He is believed to have been born in Egypt in about 10 AD. Most of his works were accomplished in Alexandria, Egypt.

## Hero's inventions

Hero developed many mechanical machines that had practical uses. They included a water organ, a fire engine, a coin-operated device, and a rocket-like device known as the aeolipile. The last of these was the earliest known steam-powered engine – a rotary steam engine that consisted of a sphere mounted on a boiler and having two canted nozzles to produce a rotary motion from the escaping steam. The siphon, known as Hero's fountain, was an instrument that produces a vertical jet of water by air pressure. The dioptra was a primitive surveying device.

It has also been suggested that Hero also built the first programmable robot. In about 60 AD, he constructed a three-wheeled cart that could carry a group of automata to the front of a stage where they would perform for an audience. Power came from a falling weight that pulled on a string wrapped round the cart's drive axle. According to Noel Sharkey, a computer scientist at the University of Sheffield, UK, this string-based control mechanism is exactly equivalent to a modern programming language.

## Hero's work in mathematics

Hero was well known for his studies in geometry and in geodesy (a branch of mathematics that searches to determine the size and shape of the Earth, and the location of objects or areas on the Earth). His most important geometric work, Metrica, was lost until a fragment was discovered in 1894, followed by a complete copy in 1896. It is a compendium, in three books, of geometric rules and formulas. In Book I appears a derivation of what is now known as Hero's formula, which expresses the area of a triangle in terms of its sides. This formula originated from Hero's attempt to demonstrate that the angle of incidence in optics is equal to the angle of reflection. Book II of the Metrica describes methods of calculating or finding the volumes of bodies such as cylinders, cones, pyramids, prisms, parallelepipeds, and spheres. Book III covers the division of volumes and areas into parts of given ratios. Hero also wrote books based on mechanics and other subjects. Among those are Automatopoietica, Pneumatica, Belopoeica, and Cheirobalistra.

Hero lived about three centuries after another ancient "rocketeer," Archytas.