on our gross atmosphere is bent out of its rectilinear course, which causes these luminaries to appear to rise sooner than they 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 co