See F. A. Aulard, _Les Orateurs de la Législative et de la Convention_ (Paris, 2nd ed., 1906).
ISOBAR (from Gr. [Greek: isos], equal, and [Greek: baros], weight), a line upon a meteorological map or pressure chart connecting points where the atmospheric pressure is the same at sea-level, or upon the earth's surface. A general pressure map will indicate, by these lines, the average pressure for any month or season over large areas. The daily weather charts for more confined regions indicate the presence of a cyclonic or anticyclonic system by means of lines, which connect all places having the same barometric pressure at the same time. It is to be noted that isobaric lines are the intersections of inclined isobaric surfaces with the surface of the earth.
ISOCLINIC LINES (Gr. [Greek: isos], equal, and [Greek: klinein], to bend), lines connecting those parts of the earth's surface where the magnetic inclination is the same in amount. (See MAGNETISM, TERRESTRIAL.)
ISOCRATES (436-338 B.C.), Attic orator, was the son of Theodorus, an Athenian citizen of the deme of Erchia--the same in which, about 431 B.C., Xenophon was born--who was sufficiently wealthy to have served the state as choregus. The fact that he possessed slaves skilled in the trade of flute-making perhaps lends point to a passage in which his son is mentioned by the comic poet Strattis.[1] Several popular "sophists" are named as teachers of the young Isocrates. Like other sons of prosperous parents, he may have been trained in such grammatical subtleties as were taught by Protagoras or Prodicus, and initiated by Theramenes into the florid rhetoric of Gorgias, with whom at a later time (about 390 B.C.) he was in personal intercourse. He tells us that his father had been careful to provide for him the best education which Athens could afford. A fact of greater interest is disclosed by Plato's _Phaedrus_ (278 E). "Isocrates is still young, Phaedrus," says the Socrates of that dialogue, "but I do not mind telling you what I prophesy of him.... It would not surprise me if, as years go on, he should make all his predecessors seem like children in the kind of oratory to which he is now addressing himself, or if--supposing this should not content him--some divine impulse should lead him to greater things. My dear Phaedrus, a certain philosophy is inborn in him." This conversation is dramatically supposed to take place about 410 B.C. It is unnecessary to discuss here the date at which the _Phaedrus_ was actually composed. From the passage just cited it is at least clear that there had been a time--while Isocrates could still be called "young"--at which Plato had formed a high estimate of his powers.