Guyot of Provence mentions mariner's compass, 21. Halske, double transmission, 114. Harmonic telegraphy, 120. receivers, 125. relay, 130. Hawksbee, Francis, electrician, 7. Heat, a mode of motion, 40. related to atoms, 42. begins and ends in matter, 44. electrical and mechanical energy the same, 46. Henry, Joseph, first practical telegrapher, 90. constructs long-distance line, 94. produces induction, 177. Heraclea and the loadstone, 20. Hertz experiments in ether-waves, 178. Homer refers to loadstone, 20. Horse-power, 214. House, Royal E., printing telegraph, 108, 110. Hughes, David E., printing telegraph, 108, 112. Induction, 56. guarded against, 169. produced by Henry, 177. Keeper of a magnet, 31. Kelvin, Lord (Sir W. Thompson), cable message receiver, 158. "Kick," in telegraphy, 115, 118. Kleist and the Leyden jar, 8. "Let her buzz," 3. Leyden jar invented, 8. Lightning, electricity; Franklin, 8. restoration of equilibrium, 78. Lightning-rods, 80. dangerous conductors, 81. Loadstone, 20, 21. Maury, Lieut., deep-sea soundings, 155. Magnes, Magnesia, 20. Magnet, electro. See Electromagnet. Magnetic earth poles, 23, 32. Magnetic lines of force, 31, 34, 60. Magnetic needle, 21. variation of, 22. dip of, 22. action of, 33. Magnetism, history of, 20. and electricity mutually dependent, 24. theories of, 24. in iron and steel, 25. in the earth, 32, 36. and sun-spots, 37. Magnetization, limit of, 31. Marconi, wireless telegraphy, 178-180. Measurement of electricity, 83. ampere, unit of, 85. method of, 86. Mercury luminous by shaking, 7. Micro-farad, unit of capacity, 119. Molecules of iron and steel natural magnets, 25. and atoms, 39. Morse, S. F. B., devises code of telegraphic signals, 95. induces Congress to construct line, 96. transmits battery current through water, 177. Motion universal, 38. causes sound, heat, light, and electricity, 39. Multiple transmission, Ch. XIII, 114. duplex, 116. quadruplex, 118. Multiple transmission, musical, 120. Musical message receivers, 125, 139. Musical tones transmitted, 91, 92, 120, 136. Muschenbroeck, Prof., and the Leyden jar, 8. Newton, Sir Isaac, electrician, 8.