Little is known about Hero, or Heron, of Alexandria except that he wrote at least thirteen books on the study and practical applications of the simple machines wedges-- levers, pulleys, and screws.
Hero is thought have lived around the time of the first century. He was a teacher of mathematics, physics, pneumatics, and mechanics at the University ofAlexandria. His published works--Pneumatics, Mechanics, Dioptra, Automata, Catoptrica, and Belopoiika--reveal him to be an inventor, especially an inventor of gadgets and automata.
In his work Pneumatics, Hero demonstrates that air is an actual substance, rather than the lack of substance. His simple experiment showed that water could not enter a container of air until air was removed. He further suggested that air was made up of individual particles separated by space and could be compressed into a smaller area. Amazingly, his ideas of gas compressionand vacuums were valid but not studied further until fifteen centuries later.
Pneumatics also contains very basic principles of steam propulsion. Infact, one of Hero's most famous inventions was the Sphere of Aeolus, two tubes attached to opposing sides of a ball. When water was boiled in the sphere,steam rose and escaped through the bent tubes resulting in a type of "whirligig" that was powered by steam. Though applied to simple automata and toys, this knowledge, too, remained dormant for seventeen centuries before it was used to ease human labor. Mechanics is largely a textbook for architects, engineers, builders, and contractors. The book was translated and publishedin German as recently as 1900 and is divided into three parts. The first part studies the theory of the wheel, proportions and scales, centers of gravity, balance and equilibrium, the statics of posts and beams, and the construction of a gear to fit an endless screw. The second part investigates the mechanical theories behind the five simple "powers" (winches, pulleys, levers, wedges, and screws) and their uses. The third section discusses uses of cranes and sledges.
In Dioptra Hero describes several instruments used by surveyors and provides mathematical background for measuring distances between sites. The book also details an odometer-like device that could measure rotations of a wheel on a level road.
Automata outlines a device that makes toys perform using an axle, strings, and drums. Catoptrica discusses mirrors and the theories of reflection and sight. Belopoiika describes crossbows and catapults.
Hero's other books briefly mention such objects as organs powered by wind orwater, thermoscopes, and coin-in-the-slot dispensing machines-- a predecessorto the parking meter!