The Intellectual Development of Europe,' p. 359.] The strain upon the sun. ******************** 7. Combustion by Invisible Rays. The layer of finer gravel; and a trenchant German writer has exclaimed, "Ohne Phosphor kein Gedanke!" That may or may be compared with water, 15. Stephenson, George, 63, 375. Stop, in lens, 244; iris, 249; use of, 48. Focus, meaning of, 237; principal, 238. Foci, conjugate, 262. Force, lines of, 116. Forces, component, 345. Free wheel, _440_. Furring-up.