Hero of Alexandria (ad20?-62?), Greek mathematician and scientist. His name is also spelled Heron. About 18 Greek writers were named Hero, or Heron, making individual identification difficult. However, Hero of Alexandria was probably born in Egypt and accomplished his work in Alexandria, Egypt. Hero wrote at least 13 works on mechanics, mathematics, and physics. He developed various mechanical devices, and many of them had practical uses. They include the aeolipile, a rotary steam engine; Hero's fountain, a pneumatic apparatus that produces a vertical jet of water by air pressure; and the dioptra, a primitive surveying instrument. He may be best known, however, as a mathematician in both geometry and geodesy (a branch of mathematics that seeks to determine the shape and size of earth, and the location of objects or areas on the earth). Hero handled problems of measurement more successfully than anyone of his time. He also devised a method of approximating the square roots and cube roots of numbers that are not perfect squares or cubes. Hero is sometimes credited with developing the formula for finding the area of a triangle in terms of its sides, but this formula was probably developed before his time.