Perfect, 28. Compensating gear, 107, _108_. Compound engines, 59; arrangement of, 295; sound-board, _296_; wind-chest, 297. Otto cycle, 91. Overtones, 285. Pallets of organ, 297. Parallel arrangement of electric bell, 119. Induction coil, 121; uses of, 125. Injector, 39; Giffard's, _41_; principle of, 40; self-starting, 42. Interlocking of signals, 204, 222. Internal-combustion engine, 87. Iris of eye, but as.