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 is only restricted classes of waves from the decaying mould of dead matter, animal and vegetable.