There are a large number of such repeater stations in the United States
along the important telephone routes. In Fig. 136 I am showing you the
location of those along the route of the famous "transcontinental
telephone-circuit." This shows also a radio-telephone connection between
the coast of California and Catalina Island. Conversations have been
held between this island and a ship in the Atlantic Ocean, as shown in
the sketch. The conversation was made possible by the use of the vacuum
tube and the bridge circuit. Part of the way it was by wire and part by
radio. Wire and radio tie nicely together because both operate on the
same general principles and use much of the same apparatus.

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INDEX

A-battery for tubes, 42

Accumulator, 29

Acid, action of hydrogen in, 7

Air, constitution of, 10

Ammeter, alternating current, 206;
calibration of, 53;
construction of, 205

Ampere, 49, 54

Amplification, 182; one stage of, 185

Amplitude of vibration, 155

Antenna current variation, 141

Arlington tests, 233

Artificial telephone line, 252

Atom, conception of, 6;
nucleus of, 10;
neutral, 34

Atomic number, 13

Atoms, difference between, 12;
kinds of, 6, 10;
motion of, 35

Attenuation of current in wires, 259

Audibility meter, 218

Audio-frequency amplifier, 185;
limitations of, 185

Audion, 35, 40, 42

Audion, amplifier, 182;
detector, theory of, 126;
modulator, 232;
oscillator, theory of, 89;
frequency control of, 99

B-battery for tubes, 43;
effect upon characteristic, 128

Banked wound coils, 228

Battery, construction of gravity, 16;
dry, 27;
reversible or storage, 29

Band of frequencies, 249

Beat note, detection of, 221, 245

Bell system, Arlington transmitter, 249

Blocking of tube, reason for, 171

Blue vitriol, 16

Bridge circuit, 255

Bureau of Standards, 50

C-battery for tubes, 46, 166;
variation of, 75;
for detection, 66

Calibration of a receiver, 214

Capacity, effect upon frequency, 100;
measurement of, 104;
unit of, 104;
variable, 107

Capacity effects, 243;
elimination of, 228

Carrier current, modulation of, 146;
telephony, 255

Characteristic, of vacuum tub