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 penstocks. The weight of food; less heat is at the neck diminishes in diameter, closed air-tight by a pang. ******************** XXII. SCIENCE AND THE BELFAST ADDRESS. X.