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A Dictionary of Greek and Roman biography and mythology (ed. William Smith) 46 46 Browse Search
Pausanias, Description of Greece 6 6 Browse Search
Diodorus Siculus, Library 2 2 Browse Search
Titus Livius (Livy), Ab Urbe Condita, books 28-30 (ed. Frank Gardener Moore, Professor Emeritus in Columbia University) 1 1 Browse Search
Pliny the Elder, The Natural History (ed. John Bostock, M.D., F.R.S., H.T. Riley, Esq., B.A.) 1 1 Browse Search
Xenophon, Memorabilia (ed. E. C. Marchant) 1 1 Browse Search
Plato, Alcibiades 1, Alcibiades 2, Hipparchus, Lovers, Theages, Charmides, Laches, Lysis 1 1 Browse Search
Plato, Parmenides, Philebus, Symposium, Phaedrus 1 1 Browse Search
Hyperides, Speeches 1 1 Browse Search
Knight's Mechanical Encyclopedia (ed. Knight) 1 1 Browse Search
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y do in reality. Euclid's treatise on optics was about 280 B. C. He is the one who told his royal master Ptolemy Philadelphus, There is no royal road to learning, sir. Ptolemy was the first to measure refractions, and is therefore the founder of an important part of optical science. — Humboldt. The magnifying power of hollow glass spheres filled with water (Seneca, 1, 6) was, indeed, as familiar to the ancients as the action of burning glasses or crystals (Aristoph. Nub. V. 765 [424 B. C.]) and Nero's emerald (Pliny, XXVII. 5). — Humboldt's Cosmos. Layard found in the ruin called Nimroud a planoconvex lens of rock-crystal 1 1/2 inches in diameter and 9/10 of an inch thick. It shows the marks of the lapidary's wheel. It gives a focus 4 1/2 inches from the plane side. Sir David Brewster says, It was used as a lens, either for magnifying or for condensing the rays of the sun. Two glass bowls were found in the same chamber. Before the discovery of the lens, it had been