Hero of Alexandria
Hero of Alexandria (/ˈhɪəroʊ/; Greek: Ἥρων[1] ὁ Ἀλεξανδρεύς, Hērōn hò Alexandreús, also known as Heron of Alexandria /ˈhɛrən/; fl. 60 AD) was a Greek mathematician and engineer who was active in Alexandria in Egypt during the Roman era. He has been described as the greatest experimentalist of antiquity[2] and his work is representative of the Hellenistic scientific tradition.[3]
Heron of Alexandria
Mathematics
Physics
Pneumatic and hydraulic engineering
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.[4][5] He is said to have been a follower of the atomists. In his work Mechanics, he described pantographs.[6] 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
Almost nothing is known about Hero's life, including his ethnicity, parents' names or occupations, birthplace, or dates. The first mention of him in extant secondary sources is a quotation of Mechanics by Pappus's Collection (4th century AD), and scholarly estimates for Hero's dates range from 150 BC to 250 AD. Otto Neugebauer noted a lunar eclipse observed in Alexandria and Rome used as a hypothetical example in Hero's Dioptra, found that it best matched the details of an eclipse in 62 AD, and surmised that Hero personally observed the eclipse from Alexandria; however, Hero does not explicitly say this, his brief mention of the eclipse is vague, and he might instead have used some earlier observer's data or even made up the example.[7]
Alexandria was founded by Alexander the Great in the 4th century BC, and by Hero's time was a cosmopolitan city, part of the Roman Empire. The intellectual community, centered on the institution of the Musaeum (which included the Library of Alexandria), spoke and wrote in Greek; however, there was significant intermarriage between the city's Greek and Egyptian populations.[8] It is assumed that Hero taught at the Musaeum, because his writings seem like course notes or textbooks in mathematics, mechanics, physics and pneumatics.
Hero described[9] 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.[10] Some historians have conflated the two inventions to assert that the aeolipile was capable of useful work, which is not entirely false, air containing a trace of water vapor. However, this engine is far from a pure aeolipile.[11]
Mathematics
Hero described a method, now known as Heron's method, for iteratively computing the square root of a number.[17] Today, however, his name is most closely associated with Heron's formula for finding the area of a triangle from its side lengths. He also devised a method for calculating cube roots.[18] He also designed a shortest path algorithm, that is, given two points A and B on one side of a line, find C a point on the straight line that minimizes AC+BC.
In solid geometry, the Heronian mean may be used in finding the volume of a frustum of a pyramid or cone.
The most comprehensive edition of Hero's works was published in five volumes in Leipzig by the publishing house Teubner in 1903.
Works known to have been written by Hero include:
Works that sometimes have been attributed to Hero, but are now thought most likely to have been written by someone else:[21]
Works that are preserved only in fragments: