(Ἥρων).

1. Of Alexandria, is called by Heron the younger (de Mach. Bell. 100.23, Fabr.) a pupil of Ctesibius, and he lived in the reigns of the Ptolemies Philadelphus and Euergetes (B. C. 284-221.) Of his life nothing is known; on his mechanical inventions we have but some scanty parts of his own writings, and some scattered notices. The common pneumatic experiment, called Hero's fountain, in which a jet of water is maintained by condensed air, has given a certain popular celebrity to his name. This has been increased by the discovery in his writings of a steam engine, that is, of an engine in which motion is produced by steam, and which must always be a part of the history of that agent. This engine acts precisely on the principle of what is called Barker's Mill : a boiler with arms having lateral orifices is capable of revolving round a vertical axis; the steam issues from the lateral orifices, and the uncompensated pressure upon the parts opposite to the orifices turns the boiler in the direction opposite to that of the issue of the steam. It is nearly the machine afterwards introduced by Avery, one of which, of six horse power, is, or lately was, at work near Edinburgh. * So says the translator of Arago's Eloge of Watt, and he adds that it is in pretty general use in Scotland. Heron's engine is described in his pneumatics presently mentioned; as also a double forcing pump used for a fire engine, and various other applications of the elasticity of air and steam. It is, however, but recently, that the remarkable claims of Heron to success in such investigations have received any marked notice. In the " Origine des Découvertes attribuées aux modernes," (3rd edition, 1796), by M. Dutens † This work is very valuable, from its giving at length every passage to which reference is made., who tries, with great learning, to make the best possible case for the ancients, the name of Heron is not even mentioned.