Silk, as insulator, 136. Single-fluid cell, 275. Single needle telegraph, Exp. 194. Sounder, telegraph, 458. Spark, 144, _a_. Static electricity, Part II. Static electric machines, 216. Steel, Chap. I.; kinds of, 2; magnetism of, 42, 46, 49. St. Elmo's fire, 222. Storage cells, 382. Successive, induction, 168; condensation, 199. Sulphuric acid, 258, 262, 314. Tangent galvanometer, 352. Telegraph, line, 459, 460; relay, 462; single needle instrument, Exp. 194; sounder, 458; static, 130. Telephone, the, 479; Bell, 480; carbon transmitter, 482; with induction coils, 483; receiver, 481. Tempering steel, 8. Temporary magnetism, 53. Terrestrial magnetism, Chap. V. Thermoelectricity, Chap. XXIV., 423. Thermopile, 425; home-made, 421. Thunder, 219. Transformers, 475. Transmitters, 480, 482. Two-fluid cell, 280, 281; care of, 282; chemical action in, 285. Two-fluid theory of electrification, 146. Unit of, current strength, 351; E. M. F., 297; of power, 355; quantity, 354; resistance, 308. Variation, angle of, 84. Varieties of electricity, 100. Volt, the, 297. Voltameters, 297, 353, 380. Water, composition of, 372. Watt, the, 355. Wheatstone's bridge, 324 to 330. Wind, electric, 155. Wire tables, Chap. XXVIII. Yoke, use of, 406. Zero, potential, 144, _a_. Zinc, chemical action with, 271; with commercial, 273. Zinc plates, reasons for amalgamating, 274. Notes. Notes. ELECTRICAL BOOKS ELECTRICAL APPARATUS GAMES PUZZLES EDUCATIONAL AMUSEMENTS [Illustration] THOMAS M. ST. JOHN, Met. E. A Word to Parents About Games and Educational Amusements. Systematic play is as important as systematic work. The best games and home amusements are as valuable to a child as school-studies; in fact, they bring out and stimulate qualities in a child, which no school-study can. Fascinating home amusements are as necessary as school-books. Boys and girls like to be busy. Their amusements should be entered into as heartily, chosen as carefully, and purchased as willingly as school-books. =Games.=--JINGO and HUSTLE-BALL are good games. They are interesting and full of action. They arouse a child's common-sense. They cultivate an ability to think rapidly, judge correctly, and decide quickly. They educate the eye and hand at the same time. They are very simple, and may be played at once. =Educational Amusements.=--There is a peculiar fascination about Electricity and Magnetism, which makes these subjects appeal to every boy and girl.