**Hero** **of Alexandria** (c. 10–70 AD) was an ancient

Greek mathematicianGreek mathematics, as that term is used in this article, is the mathematics written in Greek, developed from the 7th century BC to the 4th century AD around the Eastern shores of the Mediterranean. Greek mathematicians lived in cities spread over the entire Eastern Mediterranean, from Italy to...

and

engineerAn engineer is a professional practitioner of engineering, concerned with applying scientific knowledge, mathematics and ingenuity to develop solutions for technical problems. Engineers design materials, structures, machines and systems while considering the limitations imposed by practicality,...

Encyclopædia Britannica Online - Heron of AlexandriaEnc. Britannica 2007, "Heron of Alexandria" who was active in his native city of

AlexandriaAlexandria is the second-largest city of Egypt, with a population of 4.1 million, extending about along the coast of the Mediterranean Sea in the north central part of the country; it is also the largest city lying directly on the Mediterranean coast. It is Egypt's largest seaport, serving...

, Roman Egypt. He is considered the greatest experimenter of antiquity and his work is representative of the

HellenisticHellenistic civilization represents the zenith of Greek influence in the ancient world from 323 BCE to about 146 BCE...

scientific tradition.

Hero published a well recognized description of a

steam-powered deviceA steam engine is a heat engine that performs mechanical work using steam as its working fluid.Steam engines are external combustion engines, where the working fluid is separate from the combustion products. Non-combustion heat sources such as solar power, nuclear power or geothermal energy may be...

called an

*aeolipile*An aeolipile , also known as a Hero engine, is a rocket style jet engine which spins when heated. In the 1st century AD, Hero of Alexandria described the device, and many sources give him the credit for its invention.The aeolipile Hero described is considered to be the first recorded steam engine...

(hence sometimes called a "Hero engine"). Among his most famous inventions was a

windwheelA windmill is a machine which converts the energy of wind into rotational energy by means of vanes called sails or blades. Originally windmills were developed for milling grain for food production. In the course of history the windmill was adapted to many other industrial uses. An important...

, constituting the earliest instance of

wind harnessingWind power is the conversion of wind energy into a useful form of energy, such as using wind turbines to make electricity, windmills for mechanical power, windpumps for water pumping or drainage, or sails to propel ships....

on land. He is said to have been a follower of the

AtomistsAtomism is a natural philosophy that developed in several ancient traditions. The atomists theorized that the natural world consists of two fundamental parts: indivisible atoms and empty void.According to Aristotle, atoms are indestructible and immutable and there are an infinite variety of shapes...

. Some of his ideas were derived from the works of

CtesibiusCtesibius or Ktesibios or Tesibius was a Greek inventor and mathematician in Alexandria, Ptolemaic Egypt. He wrote the first treatises on the science of compressed air and its uses in pumps...

.

Much of Hero's original writings and designs have been lost, but some of his works were preserved in Arab manuscripts.

## 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

MusaeumThe Musaeum or Mouseion at Alexandria , which included the famous Library of Alexandria, was an institution founded, according to Johannes Tzetzes, by Ptolemy I Soter or, perhaps more likely, by Ptolemy II Philadelphus at Hellenistic Alexandria in Egypt. The Mouseion remained supported by the...

which included the famous

Library of AlexandriaThe Royal Library of Alexandria, or Ancient Library of Alexandria, in Alexandria, Egypt, was the largest and most significant great library of the ancient world. It flourished under the patronage of the Ptolemaic dynasty and functioned as a major center of scholarship from its construction in the...

, because most of his writings appear as lecture notes for courses in

mathematicsMathematics is the study of quantity, space, structure, and change. Mathematicians seek out patterns and formulate new conjectures. Mathematicians resolve the truth or falsity of conjectures by mathematical proofs, which are arguments sufficient to convince other mathematicians of their validity...

,

mechanicsMechanics is the branch of physics concerned with the behavior of physical bodies when subjected to forces or displacements, and the subsequent effects of the bodies on their environment....

,

physicsPhysics is a natural science that involves the study of matter and its motion through spacetime, along with related concepts such as energy and force. More broadly, it is the general analysis of nature, conducted in order to understand how the universe behaves.Physics is one of the oldest academic...

and

pneumaticsPneumatics is a branch of technology, which deals with the study and application of use of pressurized gas to effect mechanical motion.Pneumatic systems are extensively used in industry, where factories are commonly plumbed with compressed air or compressed inert gases...

. 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

cyberneticsCybernetics is the interdisciplinary study of the structure of regulatory systems. Cybernetics is closely related to information theory, control theory and systems theory, at least in its first-order form...

.

## Inventions and achievements

- Hero described construction of the
*aeolipile*An aeolipile , also known as a Hero engine, is a rocket style jet engine which spins when heated. In the 1st century AD, Hero of Alexandria described the device, and many sources give him the credit for its invention.The aeolipile Hero described is considered to be the first recorded steam engine...

(a version of which is known as *Hero's engine*) which was a rocket-like reaction engineA rocket engine, or simply "rocket", is a jet engineRocket Propulsion Elements; 7th edition- chapter 1 that uses only propellant mass for forming its high speed propulsive jet. Rocket engines are reaction engines and obtain thrust in accordance with Newton's third law...

and the first-recorded steam engine (although VitruviusMarcus Vitruvius Pollio was a Roman writer, architect and engineer, active in the 1st century BC. He is best known as the author of the multi-volume work De Architectura ....

mentioned the aeolipile in De Architectura' is a treatise on architecture written by the Roman architect Vitruvius and dedicated to his patron, the emperor Caesar Augustus, as a guide for building projects...

some 100 years earlier than Hero). 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
A vending machine is a machine which dispenses items such as snacks, beverages, alcohol, cigarettes, lottery tickets, consumer products and even gold and gems to customers automatically, after the customer inserts currency or credit into the 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 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
Thunder is the sound made by lightning. Depending on the nature of the lightning and distance of the listener, thunder can range from a sharp, loud crack to a long, low rumble . The sudden increase in pressure and temperature from lightning produces rapid expansion of the air surrounding and within...

was produced by the mechanically-timed dropping of metal balls onto a hidden drum.

- The force pump was widely used in the Roman
Ancient Rome was a thriving civilization that grew on the Italian Peninsula as early as the 8th century BC. Located along the Mediterranean Sea and centered on the city of Rome, it expanded to one of the largest empires in the ancient world....

world, and one application was in a fire-engine.

- A syringe
A syringe is a simple pump consisting of a plunger that fits tightly in a tube. The plunger can be pulled and pushed along inside a cylindrical tube , allowing the syringe to take in and expel a liquid or gas through an orifice at the open end of the tube...

-like device was described by Heron to control the delivery of air or liquids.

- In optics, Hero formulated the Principle of the Shortest Path of Light
In optics, Fermat's principle or the principle of least time is the principle that the path taken between two points by a ray of light is the path that can be traversed in the least time. This principle is sometimes taken as the definition of a ray 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 FermatPierre de Fermat was a French lawyer at the Parlement of Toulouse, France, and an amateur mathematician who is given credit for early developments that led to infinitesimal calculus, including his adequality...

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's fountain is a hydraulic machine invented by the 1st century inventor, mathematician, and physicist Heron, also known as Hero of Alexandria....

)

## Mathematics

Hero described a method of iteratively computing the

square rootIn mathematics, a square root of a number x is a number r such that r2 = x, or, in other words, a number r whose square is x...

. 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 numberAn imaginary number is any number whose square is a real number less than zero. When any real number is squared, the result is never negative, but the square of an imaginary number is always negative...

, or

imaginary unitIn mathematics, the imaginary unit allows the real number system ℝ to be extended to the complex number system ℂ, which in turn provides at least one root for every polynomial . The imaginary unit is denoted by , , or the Greek...

, is also noted to have been first observed by Hero while calculating the volume of a pyramidal frustum.

## Media

A 2007

The History ChannelHistory, formerly known as The History Channel, is an American-based international satellite and cable TV channel that broadcasts a variety of reality shows and documentary programs including those of fictional and non-fictional historical content, together with speculation about the future.-...

television show

*Ancient Discoveries* includes recreations of most of Heron's devices.

A 2008 The History Channel television show

*Ancient Discoveries* - "Ancient New York" includes a short recreation of a fountain device that made water flow uphill.

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

*aeolipile*, showing him as a plain craftsman who invented the

turbineA turbine is a rotary engine that extracts energy from a fluid flow and converts it into useful work.The simplest turbines have one moving part, a rotor assembly, which is a shaft or drum with blades attached. Moving fluid acts on the blades, or the blades react to the flow, so that they move and...

accidentally.

## See also

- Heron's formula
- Heronian triangle
In geometry, a Heronian triangle is a triangle whose sidelengths and area are all rational numbers. It is named after Hero of Alexandria. Any such rational triangle can be scaled up to a corresponding triangle with integer sides and area, and often the term Heronian triangle is used to refer to...

- Heronian mean
- Heron's engine

## External links