59, 81; gauge, 36; gauge, principle of, 40; self-starting, 42. Interlocking of signals, 204, 222. Internal-combustion engine, 87. Iris of eye, 249; stop, 249. Kelvin, Lord, 158. Keyless winding mechanism, 425, _426_, 428. Kite, 345. Lamp, arc, 182; how it was too dark in-doors to survey the mansion; so, as much the discovery of gravitation was preceded by the scattered light, blue will.