212. Sparking-plug, _102_. Spectacles, use of, 48. Focus, meaning of, 325; simple, _328_; wheel, _327_. Beau de Rochas, 89. Bell, diving, _332_; electric, 119, _120_. Bellows of organ, 298. Pelton wheel, _377_. Pendulum, 412; compensating, 418, _419_. Perilymph, 272. Perry, Professor, 16. Petrol, 98. Phonograph, 310; governor, _311_; recorder, 312, _313_; records, making of, 319; reproducer, 315; tracings on record of, _317_. Pianoforte, 277; sounding-board.