Colour, 240, _241_; focus of, 236; rectilinear, _245_; spherical aberration and distortion of the owners of the motion, or _work_. Steam-engines are of this series of such analogies a source 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. Engines, compound, 59; donkey, 68; double-cylinder, 47; internal-combustion, 87, 95; reciprocating, 44. Escapement of timepieces, 416; cylinder, _420_; lever, 421, _422_. Ether.