Acetylene gas at Niagara, 230.
Alexandria, temple with loadstone, 20.
Amber—elektron, 6.
AmpÈre, theory of magnetism, 25.
unit of electrical current, 85.
galvanometer, 93.
Aluminum at Niagara, 223.
Arabians, magnetic needle, 21.
Arago, germ of electromagnet, 93.
Aristotle mentions torpedo, 6.
refers to magnet, 20.
Atmospheric electricity, Ch. VIII, 77.
Atoms and molecules, 39.
of substances differ in weight, 42.
relations to heat, 42.
Aurora Borealis, 35.
Bain chemical telegraph register, 101.
Barlow on galvanism in telegraphy, 93.
Bell, Alexander Graham, radiophone, 171.
Bleaching-powder at Niagara, 218.
Branly invents the coherer, 179.
Cables, submarine. See Submarine Cables.

Calcium-carbide at Niagara, 228.
Capacity of a circuit, 118, 119.
Caustic soda, 221.
Chinese, magnetic needle, 21.
Chlorine and sodium, 219.
Circuit-breaker at Niagara, 199.
Closed circuit and current, 122.
Coherer (wireless telegraphy), 179.
Columbus, compass variations, 22, 34.
Condenser in resistance-coil, 118.
in Morse relays, 131.
Conductors and non-conductors of electricity, 47.
relation to electric light, 50.
different resistances, 74, 83.
Cooke, needle telegraph, 108.
Crookes, Prof., X-ray, 121.
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.
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.
ampÈre, 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