# Hero of Alexandria

Hero (or Heron) of Alexandria (c. 10–c. 70) was a Greek engineer and geometer. His most famous invention was the first documented steam engine, the aeolipile. He is said to have been a follower of the Atomists. Some of his ideas were derived from the works of Ctesibius.

A number of references mention dates around 150 BC, but these are inconsistent with the dates of his publications and inventions. This may be due to a misinterpretation of the phrase "first century".

## Publications

The complete surviving works are

• Pneumatica (Greek, c. 60),
• Automata (Greek),
• Mechanics (Arabic),
• Metrics (Arabic),
• Dioptra (Arabic).

In optics, Hero proposed that light travels along the shortest geometric path. This view is no longer accepted, having been replaced by the least-time principle.

In geometry, he is credited with the Heron's formula, though he did not actually prove it. He also came up with an iterative process for calculating square roots of numbers.

Hero is credited with inventing many feedback control devices using water, fire and compressed air in various combinations, and the first type of analogue computer programming via intricate systems of geared spindles studded with pegs and wound with ropes connected to weights (trays of sand emptying over time) used to operate his automatic theaters that included automatic doors and multiple changing scenes of moving figures accompanied by lighting and sound effects.

## Projects

• steam turbine (50/62/70) (aeolipile) - the first recorded steam engine, which was created almost two millenia before the industrial revolution, which was powered by steam engines. Apparently Hero's steam engine was taken to be no more than a toy, and thus its full potential not realized for quite some time.
• automatic temple doors - controlled by the temple priest lighting an altar outside of the temple, which heated water beneath it, which then moved counterweights which would open the doors. When the fire was extinguished, the water would cool and thus return the counterweights to their original position, which closed the temple doors.
• Coin operated Vending Machine - to vend holy water for temple worshipper to cleanse their hands
• Machine gun (which fired arrows), mechanical bow (which could fire arrows with great strength), and hand-powered catapult - these were designed but not realized because the needed materials were not yet available.
• water organ or hydraulic organ
• automated puppet theatres
• omen machine - temple patrons asked a simple yes or no question, and by descretion of the priest, the answer was yes or no depending on whether the mechanical bird sitting on the top of the box would sing and twirl or not
• water-powered mechanical birds - this was used in Hero's omen machine as well as entire flocks of mechanical birds. Realistic chirping sound effects also produced by a water device.
• compressed-air fountain
• siphons - this powered many of Hero's projects
• machine for threading wooden screws
• automated machine for moving full-scale theater set pieces
• density of air
• odometer
• naval log, a variation of the odometer to be used at sea