# 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, England, 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 concerned with determining the size and shape of Earth,
and the location of objects or areas on 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 (see laws 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.