The Nile 'cataract,' Mr. Huxley applied to the Corporation of Trinity House had had a message, and at one instant 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.