HERON, 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 Heron'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 HERON, by Augustus de Morgan, in Smith's Dict. of Biog.) 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 Baruleus, an essay on the lifting of heavy weights; his essay on the Construction of Automata; his Chiroballistra, and his Belipeica, 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.