Lock, _436_, _437_. Yellow spot, in eye, 251. Spring balance for watches, 415. Gooch reversing gear, 65. Governors, speed, 67; of motor cars, 109. Siphon, _351_. Slide-valve, 49, 50, 51; setting of, 53. Sliders, 297. Sound, nature of, 270; board of piano, 283. Advancing the spark, 102. Air-gun, _342_. Air-pump for cycle tyres, _340_; for Westinghouse brake, 199. Alternating currents, 164; dynamo.