Hero (or Heron) of Alexandria (Ήρων ο Αλεξανδρεύς) (c. 10–70 AD) was an ancient Greek mathematician and engineer who was active in Alexandria, Ptolemaic Egypt. He is considered the greatest experimenter of antiquity and his work is representative of the Hellenistic scientific tradition.

Among his most famous inventions were the first documented steam-powered device, the aeolipile, and a windwheel, constituting one of the earliest instances of wind harnessing. He is said to have been a follower of the Atomists. Some of his ideas were derived from the works of Ctesibius.

Background

Due to strong Babylonian influence in Hero's work it was once speculated by a minority of scholars that Hero may have been a Greek of Egyptian or Phoenician origin, but the modern scholarly consensus is that he was a pure Greek. The historian of mathematics C. B. Boyer explains that Hero's identification as an Egyptian or a Phoenician was largely due to the strong Babylonian influence on his work. However at least from the days of Alexander the Great to the close of the classical world, there undoubtedly was much intercommunication between Greece and Mesopotamia, and it seems to be clear that the Babylonian arithmetic and algebraic geometry continued to exert considerable influence in the Hellenistic world.

Career

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 Hero was a common name.

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 20th century, it is thought that the work of Hero, his "programmable" automated devices in particular, represents some of the first formal research into cybernetics.

Hero was known for his amazing mechanical ingenuity in the ancient world, including his contributions in military technology and theatre. He also created devices used in temples to instill faith by deceiving believers.

Inventions and achievements

• The aeolipile (known as Hero's engine) was a rocket-like reaction engine and the first recorded steam engine. 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 windwheel operating an organ, marking probably the first instance of wind powering a machine in history.
• Hero 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.
• The syringe described by Heron controlled 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 Ibn al-Haytham expanded the principle to both reflection and refraction, and the principle was not stated in this form until Pierre de Fermat did so 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)

Mathematics

Heron described a method of iteratively computing the square root. It is also called the Babylonian method, because the Babylonians also knew of it before Heron wrote it down. Today, though, his name is most closely associated with Heron's Formula for finding the area of a triangle from its side lengths.

Bibliography

The most comprehensive edition of Hero's works was published in 5 volumes in Leipzig by the publishing house Teubner in 1903.

Works known to be written by Hero:

• Pneumatica, a description of machines working on air, steam or water pressure, including the hydraulis or water organ.
• Automata, a description of machines which enable wonders in temples by mechanical or pneumatical means (e.g. automatic opening or closing of temple doors, statues that pour wine, etc.). See Automaton.
• Mechanica, preserved only in Arabic, written for architects, containing means to lift heavy objects.
• Metrica, a description of how to calculate surfaces and volumes of diverse objects.
• On the Dioptra, a collection of methods to measure lengths. In this work the odometer and the dioptra is described, an apparatus which resembles the theodolite.
• Belopoeica, a description of war machines.
• Catoptrica, about the progression of light, reflection and the use of mirrors.

Works which have sometimes been attributed to Hero, but are now thought to have most likely been written by someone else:

• Geometria, a collection of equations based on the first chapter of Metrica.
• Stereometrica, examples of three dimensional calculations based on the second chapter of Metrica.
• Mensurae, tools which can be used to conduct measurements based on Stereometrica and Metrica.
• Cheirobalistra, about catapults.
• Definitiones, containing definitions of terms for geometry.

Works which are preserved only in fragments:

• Geodesia
• Geoponica

Latest paper on Hero:

• Schellenberg, H.M.: Anmerkungen zu Heron von Alexandria und seinem Werk über den Geschützbau, in: Schellenberg, H.M./ Hirschmann, V.E./ Krieckhaus, A.(edd.): A Roman Miscellany. Essays in Honour of Anthony R. Birley on his Seventieth Birthday, Gdansk 2008, 92-130 (with a huge bibliography of over 300 titles and discussion of the communis opinio on Hero).

Media

A 2007 The History Channel television show Ancient Discoveries includes recreations of most of Heron's devices.

A 1979 Soviet animated short film focuses on Heron's invention of the aeolipile.

See also

• Heron's formula
• Heronian triangle
• Heronian mean
• Hero's engine (Aeolipile)
• Heron's fountain
• Al-Jazari

References

External links

• Webpage about Hero by The Technology Museum of Thessaloniki
• A translation of Pneumatica with diagrams
• Heron, and a translation of Pneumatica in German
• Heron biography, The MacTutor History of Mathematics archive
• Shockwave-Applet: Herons trumpet signal