Page. Aberration, spherical, of lens, 243. Acoustics, 294. Achromatic lens, 243. Acoustics, 294. Achromatic lens, 243. Acoustics, 294. Achromatic lens, 243. Action carriage of piano, 280. Spagnoletti disc instrument, 212. Sparking-plug, _102_. Spectacles, use of, 48. Focus, meaning of, 237; principal, 238. Foci, conjugate, 262. Force, lines of, 116. Forces, component, 345. Free wheel, _440_. Furring-up of pipes, 391. Fusee, drum and, 414. Galileo.