EUCLID (300 B.C.) compressed in one volume all the geometrical knowledge extant, adding several original theorems. His “Elements” has been translated into many languages, and though it has attained the venerable age of 2,200 years, its clear demonstrations are still standards in our schools. ARCHIMEDES was educated in Alexandria, but afterward lived in Syracuse, where his mathematical genius challenged the admiration of the world. In geometry and mechanics he was the master-mind of antiquity; and until the star of Newton rose twenty centuries after, Europe saw not his equal. Many important discoveries in physical science are due to Archimedes,—the principle of the lever, which led him to exclaim, “Give me a place to stand on, and I will move the world;” the process of finding the specific gravity of bodies; the hydraulic screw and the pulley. Of his many mathematical works, written in Doric Greek, eight survive. ERATOSTHENES (276-196 B.C.) was the founder of geodesy and chronology, as well as a proficient in astronomy, grammar, and poetry. The ancients styled him _Pentathlos_ (_quintuple athlete_); also, from his determining the magnitude of the earth, “Measurer of the Universe.” His most important works are “Chronographies,” and geographical and mathematical writings. HIPPARCHUS (150 B.C.), an astronomer of the Alexandrian age, deserves mention as the inventor of the planisphere and as the first to make a catalogue of the stars. He devised the method of locating places by latitude and longitude. =Grammar.=—The Museum was especially eminent as a school of grammar and criticism, the principal occupation of its scholars being the revision and correction of the texts of the old authors. The most distinguished of the Alexandrian critics were—ZENOD’OTUS, the first librarian and critical editor of Homer’s epics; ARISTOPHANES OF BYZANTIUM, his pupil (200 B.C.), the inventor of Greek accents and punctuation; ARISTARCHUS (156 B.C.), “the arch-grammarian of Greece,” who divided Homer’s poems into books, revised the Alexandrian canon, and was the author of 800 commentaries; and CRA’TES, head of a grammatical school at Pergamus, and the first to make grammar a popular study at Rome. =History.=—POLYBIUS (204-122 B.C.) was the chief historian of the Alexandrian age. Brought to Rome a prisoner after the battle of Pydna (168 B.C.), in which the king of Macedon was overthrown by Paulus Æmilius, he became the intimate friend of Scipio Africanus the Younger. Seventeen years elapsed before Polybius was permitted to return to Greece. Then he went back the firm friend of the Romans; and had his countrymen heeded his counsels, the sack of Corinth might have been averted and Greece might have preserved her independence. So, at least, declared the inscription on his statue: “Hellas would have been saved had she followed the advice of Polybius.”