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Heronn of Alexandria (c. 10 70 AD) was an ancient Greek mathematician and engineer who was active in his native city of Alexandria, Roman Egypt. He is considered the greatest experimenter of antiquity and his work is representative of the Hellenistic scientific tradition.
Heron published a well recognized description of a steam-powered device called an aeolipile (hence sometimes called a "Heron engine"). Among his most famous inventions was a wind wheel, constituting the earliest instance of wind harnessing on land. He is said to have been a follower of the Atomists. Some of his ideas were derived from the works of Ctesibius.
Much of Heron's original writings and designs have been lost, but some of his works were preserved in Arab manuscripts.
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" or because Heron was a common name.
It is almost certain that Heron taught at the Museum which included the famous Library of Alexandria, because most of his writings appear as lecture notes for courses in mathematics, mechanics, physics and pneumatics. Although the field was not formalized until the 20th century, it is thought that the work of Heron, his automated devices in particular, represents some of the first formal research into cybernetics. Heron described construction of the aeolipile (a version of which is known as Heron's engine) which was a rocket-like reaction engine and the first-recorded steam engine (although Vitruvius mentioned the aeolipile in De Architectura some 100 years earlier than Heron). It was created almost two millennia before the industrial revolution. Another engine used air from a closed chamber heated by an altar fire to displace water from a sealed vessel; the water was collected and its weight, pulling on a rope, opened temple doors. Some historians have conflated the two inventions to assert that the aeolipile was capable of useful work. The first vending machine was also one of his constructions, when a coin was introduced via a slot on the top of the machine; a set amount of holy water was dispensed. This was included in his list of inventions in his book, "Mechanics and Optics". When the coin was deposited, it fell upon a pan attached to a lever. The lever opened up a valve which let some water flow out. The pan continued to tilt with the weight of the coin until it fell off, at which point a counter-weight would snap the lever back up and turn off the valve. A wind wheel operating an organ, marking the first instance of wind powering a machine in history. Heron also invented many mechanisms for the Greek theater, including an entirely mechanical play almost ten minutes in length, powered by a binary-like system of ropes, knots, and simple machines operated by a rotating cylindrical cogwheel. The sound of thunder was produced by the mechanically-timed dropping of metal balls onto a hidden drum. The force pump was widely used in the Roman world, and one application was in a fire-engine.
A syringe-like device was described by Heron to control the delivery of air or liquids. In optics, Heron formulated the Principle of the Shortest Path of Light: If a ray of light propagates from point A to point B within the same medium, the path-length followed is the shortest possible. It was nearly 1000 years later that Alhacen expanded the principle to both reflection and refraction, and the principle was later stated in this form by Pierre de Fermat in 1662; the most modern form is that the path is at an extremum. A standalone fountain that operates under self-contained hydrostatic energy. (Heron's fountain).
Heron described a method of iteratively computing the square root. Today, though, his name is most closely associated with Heron's Formula for finding the area of a triangle from its side lengths.
The imaginary number, or imaginary unit, is also noted to have been first observed by Heron while calculating the volume of a pyramidal frustum.

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Last updated: July 30, 2012