_296_; wind-chest, 297. Otto cycle, 91. Overtones, 285. Pallets of organ, 296; board of piano, 280. Spagnoletti disc instrument, 212. Sparking-plug, _102_. Spectacles, use of, 48. Focus, meaning of, 325; simple, _328_; wheel, _327_. Beau de Rochas, a Frenchman, first thought of devising means whereby.