a mathematician and natural philosopher of Alexandria, was the pupil of Ctesibius, and flourished B.C. 284–221. His name has been preserved in the well-known experiment of Hero's Fountain, in which, by means of condensed air, water is made to spring from a jet in a continuous stream. The loss of some of Heron's works is matter of much regret. In those that survive mention is made of a steam-engine which seems to have been set in motion exactly on the principle of what is popularly known as Barker's Mill. It is only recently, however, that Heron's claims have found an advocate, and it is expected that further researches will bring to light results in the meantime quite unlooked for. (See Hero, by Augustus de Morgan, in Smith's Dict. of Biogr.) Heron's most valuable work is that on Pneumatics, in which are given his experiments on the elasticity of the air and of steam. Besides his Pneumatics may be mentioned his Baroleus, an essay on the lifting of heavy weights; his essay on the Construction of Automata; his Chiroballistra, and his Belizea, which treat of the artillery of the ancients; and a fragment on Dioptries. Most of these works are to be found in the Mathematici Veteres, Paris, 1693.

Hero, called the younger, to distinguish him from his namesake of Alexandria, was, like him, a mathematician and natural philosopher. His birthplace, or even his country, is quite unknown, and even his floruit is only guessed to have been contemporaneous with that of the Emperor HERACLIUS, A.D. 610-641. The writings assigned to this Heron are a treatise on Geodesia, or practical geometry; another on the Terms of Geometry; and some works on various military matters, such as The Attack and Defence of Towns; the Machines of War. Some of these works appear in the Mathematici Veteres; others are printed separately; and some are still in MS.

See index to Ornithology.