Hero (or Heron) of Alexandria (Greek: Ἥρων ὁ Ἀλεξανδρεύς) (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.
Hero published a well recognized description of a steam-powered device called an aeolipile (hence 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. Some of his ideas were derived from the works of Ctesibius.
Much of Hero'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 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 automated devices in particular, represents some of the first formal research into cybernetics.
Hero 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 Hero while calculating the volume of a pyramidal frustum.
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 Heron:
- 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, an apparatus which resembles the theodolite, are described.
- 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.
- Cheiroballistra, about catapults.
- Definitiones, containing definitions of terms for geometry.
Works which are preserved only in fragments:
Latest paper on Hero:
- Schellenberg, H.M.: Anmerkungen zu Hero 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).
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