Fig. 70.--Action of Two-electrode Vacuum Tube

(A) and (B) Fig. 71.--How a Two-electrode Tube Acts as Relay or a
Detector

(C) Fig. 71--Only the Positive Part of Oscillations Goes through the
Tube

(A) and (B) Fig. 72.--How the Positive and Negative Voltages of the
Oscillations Act on the Electrons

(C) Fig. 72.--How the Three-electrode Tube Acts as Detector and
Amplifier

(D) Fig. 72.--How the Oscillations Control the Flow of the Battery
Current through the Tube

Fig. 73.--How the Heterodyne Receptor Works

Fig. 74.--Separate Heterodyne Oscillator

(A) Fig. 75.--Apparatus for Experimental C. W. Telegraph Transmitter.

(B) Fig. 75.--Apparatus for Experimental C. W. Telegraph Transmitter.

Fig. 76.--Experimental C. W. Telegraph Transmitter

Fig. 77--Apparatus of 100-mile C. W. Telegraph Transmitter