Directly profitable, "and the backward state of intense white heat, by the condensation of incandescent lamps, 180. Lap of slide-valve, _57_, 59. Larynx, 306. Laxey wheel, _380_, 381. Leads, 208. Lenses, 231; correction of for colour, 240, _241_; focus of, 236; rectilinear, _245_; spherical aberration in, 243. Levers, signal, colours of, 230. Speed governors, 67, _68_, _69_; Hartwell, 70; marine, 71. Speed of motor.