63, 375. Stop, in lens, 244; iris, 249; use of, 249. Spectrum, colours of, 230. Speed governors, 67, _68_, _69_; Hartwell, 70; marine, 71. Speed of motor cars, 110. Spot, blind, in eye, 251; yellow, in eye, 251. Spring balance for watches, 419; compensating, 423, _424_. Stapes, 272. Steam, what it is: I shouldn't wonder if the united affluents of.