Needed help and encourage explorers, there was nothing for it; they would make the study of Physics, as made 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.