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Ancient Greek Scientists
HERO OF ALEXANDRIA (fl. 1st century BC)

Hero of Alexandria was a celebrated mathematician, physicist and engineer who lived in the 1st century BC. He set up and directed the Higher Technical School of Alexandria, which he developed into a genuine Polytechnic. Often referred to as the "encyclopaedist", he built on and developed the theoretical and practical work of Ctesibius, whose famous constructions place him among the greatest figures in mechanical engineering in the ancient world.

Hero wrote extensively, on several branches of geometry, land surveying, mechanics and optics. His works include: "Geometry", "Definitions", "Stereometry", "Engines of War", "Winches", "Ballistics", "Reflections". Many of his works have been lost, while others survive in fragments in Greek or Latin. Five complete works survive: "Pneumatics" and "Automata" in Greek and "Mechanics", "Metrics" and "Dioptra" in Arabic.

Hero is best known today for his famous mechanical "Fountain", and for his formula for finding the area of a triangle from the length of the sides. His most important invention, however, was the aeolipile, a steam-powered engine. His "Dioptra" is a work on land surveying, and is considered one of the best of its kind. He was a skilled draughtsman, and his works are decorated with a wealth of sketches that make them wholly priceless. His language is simple, his thinking energetic and his teaching straightforward, all of which helped make his works extremely popular and contributed to their dissemination. Many of them were translated, first into Arabic and then into Latin, and they constituted the foundation of mechanics and related sciences until the 18th century.

- The discovery of the steam-engine.

Although there are indications that Archimedes and Philo made some simple use of steam, the discovery of the steam engine definitely belongs to Hero. In the history of mechanics, the rotating device invented by Hero is known as an aeolipile or steam sphere or wind ball. The principle was very simple: a large sealed cauldron of water was placed over a source of heat. As the water boiled, steam rose into two pipes, between which was pivoted a sphere. Jets of steam escaped from the sphere through two L-shaped outlets, sending it spinning around at great speed. This remarkable device was used in many different mechanisms and constructions, but was never developed to the point where it became as important a discovery as Papin's steam-powered piston in 1681. This was largely because the power of steam was considered a paradoxical phenomenon and not a dynamic state. Nonetheless, the repeated discovery of the power of steam, from Leonardo da Vinci with his 'architron', a steam cannon based on an invention of Archimedes, to Papin and his pressure cooker, owe much to the ancient Greek mechanical engineers: Archimedes, Philo (who invented a steam siren for lighthouses) and Hero, not to mention Philomenes, who in 250 BC built a steam pressure vessel very like that of Papin, although without the latter's safety valve. Papin corresponded with Leibnitz, who had translated Hero's work on pneumatics, in which he describes his aeolipile. This is just one more indication of the Greek contribution to the discovery of the steam engine.

- The odometer and the naval log.

The odometer is first described by Vitruvius, who devotes a whole chapter to it. This shows the importance of the device, which Vitruvius says was "transmitted to us by our predecessors". Vitruvius, however, was referring to a roughly similar device that was probably either designed or made by Archimedes. This, apart from a brief reference in John Tsetses much later, is the only evidence connecting Archimedes with the odometer. Hero, by contrast, describes it in detail in chapter 34 of his "Dioptra", where he describes it as a an adjunct to the dioptra. His odometer was a set of toothed wheels that used an endless screw to transmitt the forward progress of the vehicle's wheels and convert it into units of length. The distance travelled could then be read off a graduated table on the upper surface of the box housing the mechanism: something like the taximeter to which modern researchers have humorously compared it.

The naval log mentioned by Hero in paragraph 38 of his "Dioptra" was a variation on this device. A paddlewheel on a float fitted to the outside of the hull was connected to a mechanism like that described for the odometer, located inside the vessel. The final wheel in the series made a full revolution every Roman mile, or about 1400 metres. Both these instruments were important and very useful inventions, especially the naval variant, which improved the measurement of distances at sea. The naval log was replicated by K. N. Rados in wood and brass and exhibited at the International Exhibition in Bordeaux in 1907. The odometer was reconstructed recently by Dutch engineer Andre Sleeswyk, who presented it at a special congress on technology held in Athens in 1987.

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