Expansive working of steam, 56. Faraday, Michael, 159. Field, magnetic, 159; magnets, 171; ring, 174. Filters, 374; Maignen, 373 ; Berkefeld, 374. Filtration beds, 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;
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