E. M. F., [59];
alternating, [76];
of self-induction, [238]
Energy, expended in tube, [235];
of electrons, [113];
radiation of, [125]
Ether, [88]
Feed-back circuit, [182]
Frequency, [98], [158];
effect upon pitch, [133];
interval, [247];
natural, [117];
of voice, [163]
Fundamental note, of string, [157]
Gravity battery, theory of, [23]
Grid, action of, [47];
condenser, [169];
current, [173];
leak, [171];
leak, construction, [172], [216];
of audion, [41]
Harmonics, [160]
Helium, properties of, [9]