372. Flute, 308. Flying-machines, 348. Fly-wheel, 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, 259, 325, 416. Galilean telescope, _259_. Gas, coal, 394; governor, 402; meter, 405; traps, 374; works, 394. Gasometer, 397; largest, _398_, 399. Gauge, steam, 36, _38_; water, 35, _36_. Gear, compensating, 107, _108_. Compound engines, 59; arrangement of, 295; sound-board, _296_; wind-chest, 297. Otto cycle, 91. Overtones, 285. Pallets of organ, 296; board of piano, 283. Advancing the spark, 102. Air-gun, _342_. Air-pump for cycle tyres, _340_; for Westinghouse brake, 199. Alternating currents, 164; dynamo, 164. Amperage, 125. Angle of advance, 57.