art of preparing, preserving, and compounding medicines. See Materia Medica. See also Prescriptions, Extemporaneous.

Pharos, (Homer, Strabo, &c.), a small oblong island, Pharos island, adjoining to the continent of Egypt, over-against Alexandria. On this island stood a cognominal light-tower, of four sides, each side a stadium in length; and the tower so high as to be seen 100 miles off. Some affirm, each of its four corners rested on a large sea-crab of glass or of hard transparent stone of Ethiopia or Memphis. Others imagine the crabs were only added externally to the base by way of ornament, or as emblematical of its situation and use. The architect was Sostrates the Cnidian, as appears by an inscription on the tower, under Ptolemy Philadelphus, who laid out 800 talents upon it. On account of the port of Alexandria, the entrance to which was difficult and dangerous, the Pharos was called the key of the Egyptian sea, or even of Egypt itself (Lucan); and Pharos, from being a proper name, became an appellative to denote all lighthouses.