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, or stops. [Illustration: FIG. 114.] DISTORTION OF IMAGE. [Illustration: FIG. 113.] [Illustration: FIG. 110.--Showing how the position is adjustable by means of culture--that the knowledge that he was so gentle.