Heron of Alexandria (probably 1st—2nd centuries AD) was an ancient Greek scholar and engineer. He taught in Alexandria.
Almost all of his extensive scientific works have come down to us. In them Heron set out the main achievements of his ancient predecessors in the field of applied mechanics. His two-volume work “Pneumatica” was especially popular; it describes a variety of mechanisms in which heated or compressed air and steam were used, in particular the aeolipile (the first working steam engine, a distant ancestor of the modern reaction turbine), an automatic device for opening doors, a fire pump, siphons and so on.
In “Mechanics” Heron examined in detail the simple machines — the windlass, the lever, the pulley, the wedge, the screw and gear trains — and more complex mechanisms as well. This work was a kind of encyclopedia of ancient technology. In the work “On the Dioptra” he described instruments for measuring angles and distance travelled, the dioptra and the hodometer, and in the work “Catoptrica” he put forward an idea analogous to Fermat's principle in optics (the path of a ray on reflection is the shortest one).