Cuneus and the Leyden jar, 8. Curiosities, Ch. XX, 171. Daniell battery, 85. Differential magnet, 115. Dinocares and the loadstone, 20. Dolbear, Amos E., wireless telegraphy, 178. Dupay discovers positive and negative electricity, 8. Duplex telegraphy, 114. Dynamo-electric machines, 67. invented by Faraday, 14, 69. usual construction, 70. at Niagara, 192. Double transmission, 115. Earth electric currents, in telegraphy, 99, 116, 182. Earth magnetism, 32. effects of, on iron, 35. Aurora, 35. telegraph-lines, 36. from sun's heat, 75. Edison, Thomas, railway telegraphy, 131. electromotograph, 175. Electric currents, Ch. VI, 49. not currents but atomic motion, 54. induction of, 56. guarded against, 169. at Niagara, 193. Electric generators, Ch. VII, 62. frictional, 49. galvanic batteries, 62. storage-batteries, 64. dynamos, 67, 192. metal heating, 74. Electricity, science of, 6. achievements of, 16. eras in science of, 18. theory of, Ch. V, 39. not a fluid, a form of energy, 40. static and dynamic, 46. measurement of, Ch. IX, 83. Electric light, cause of, 50. Electric machines, 49. frictional, 51. galvanic or chemical, 51. mechanical, 70. Electromagnet invented by Faraday, 14. commercial value, 23. theory of (soft iron), 26. permanent (steel), 28. condition of use, 30. the earth a, 32. germ of, 93. differential, 115. Electromotograph, 175. Ellsworth, Miss, sends first telegraphic message, 96. Ether, lines of force, 31. nature of, 40. Ether, impressed by atomic motion, 56. inducing electric action, 56. Farad, unit of capacity, 118. Faraday, Michael, 14. Farmer, Moses G., double transmission, 114. Field, Cyrus W., lays first Atlantic cable, 156. Field of a magnet, 31. Fitzgerald, Niagara Falls chemist, 210. Franklin catches the lightning, 8. identity of lightning and electricity, 10. kite experiment, 11. electric firing-telegraph, 88. Frode, history of Iceland, 21. Gadenhalen uses magnetic needle 868 A.D., 21. Galileo's seed-thought, 89. Galvani, Luigi, and galvanism, 12. Galvanic batteries, 62. author's experience, 65. Galvanometer, 75, 93. Gilbert, Dr., frictional electricity, 7. Gintl, double transmission, 114. Gray, Elisha, constructs voltaic pile, 65. electrically transmits music, 91. experiments on transmission of music, articulate speech, and multiple messages, 123. files telephone caveat, 135. musical experiments, 136. speech receivers, 139. boys' telephone, 141. first telephone specification on record, 143. dial-telegraph, 161. automatic-printing telegraph, 163. telautograph, 165. electric musical receiver, 175. Gray, Stephen, electrician, 8. Grier, John A., quoted, 67.