Hero of Alexandria ( Heron ho Alexandreus; also known as Heron of Alexandria c. 10 AD – c. 70 AD) was a Greco-Egyptian mathematician and engineer who was active in his native city of Alexandria, Roman Egypt. He is often considered the greatest experimenter of antiquity and his work is representative of the Hellenistic scientific tradition.
Hero published a well-recognized description of a steam-powered device called an aeolipile (sometimes called a “Hero engine”). Among his most famous inventions was a windwheel, constituting the earliest instance of wind harnessing on land. He is said to have been a follower of the atomists. In his work Mechanics, he described pantographs. Some of his ideas were derived from the works of Ctesibius.
In mathematics, he is mostly remembered for Heron’s formula, a way to calculate the area of a triangle using only the lengths of its sides.
Much of Hero’s original writings and designs have been lost, but some of his works were preserved including in manuscripts from the Eastern Roman Empire and to a lesser extent, in Latin or Arabic translations.
LIFE AND CAREER
Hero’s ethnicity may have been either Greek or Hellenized Egyptian. It is almost certain that Hero taught at the Musaeum 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 twentieth century, it is thought that the work of Hero, in particular his automated devices, represented some of the first formal research into cybernetics.
Hero described the construction of the aeolipile (a version of which is known as Hero’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 Hero). It was described 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 in history of wind powering a machine.
- Hero also invented many mechanisms for the Greek theatre, 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 Hero to control the delivery of air or liquids.
- In optics, Hero 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 optical path is stationary.
- A stand-alone fountain that operates under self-contained hydro-static energy; now called Heron’s fountain.
- A programmable cart that was powered by a falling weight. The “program” consisted of strings wrapped around the drive axle.