From spherical aberration in, 243. Levers, signal, colours of, 208. Limit of error in cylinder, 52. Light, electric, 179; nature of, 112; static, 114. Electric bell, 119, _120_; signalling, 225; slot, 226. Electroplating, 185, _186_. Electro-magnets, 117. Endolymph, 272.