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ISABNORMAL (or Isanomalous) LINES, in physical geography, lines upon a map or chart connecting places having an abnormal temperature. Each place has, theoretically, a proper temperature due to its latitude, and modified by its configuration. Its mean temperature for a particular period is decided by observation and called its normal temperature. Isabnormal lines may be used to denote the variations due to warm winds or currents, great altitudes or depressions, or great land masses as compared with sea. Or they may be used to indicate the abnormal result of weather observations made in an area such as the British Isles for a particular period.

ISAEUS (c. 420 B.C.-c. 350 B.C.), Attic orator, the chronological limits of whose extant work fall between the years 390 and 353 B.C., is described in the Plutarchic life as a Chalcidian; by Suidas, whom Dionysius follows, as an Athenian. The accounts have been reconciled by supposing that his family sprang from the settlement (κληρουχία) of Athenian citizens among whom the lands of the Chalcidian hippobotae (knights) had been divided about 509 B.C. In 411 B.C. Euboea (except Oreos) revolted from Athens; and it would not have been strange if residents of Athenian origin had then migrated from the hostile island to Attica. Such a connexion with Euboea would explain the non-Athenian name Diagoras which is borne by the father of Isaeus, while the latter is said to have been “an Athenian by descent” (Ἀθηναῖος τὸ γένος). So far as we know, Isaeus took no part in the public affairs of Athens. “I cannot tell,” says Dionysius, “what were the politics of Isaeus—or whether he had any politics at all.” Those words strikingly attest the profound change which was passing over the life of the Greek cities. It would have been scarcely possible, fifty years earlier, that an eminent Athenian with the powers of Isaeus should have failed to leave on record some proof of his interest in the political