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500 RICHARDSON'S BLUEBOOK OF PROJECTION
(18) Hence bulb No. 1 acts as a switch that opens automatically every time its plate becomes negative, and closes automatically every time the plate becomes positive. This is the action of any rectifying tube.
Let us for a moment longer continue to forget bulb No. 2, and concentrate on bulb No. 1. The circuit we have just traced is a complete rectifying circuit. Assume that a storage battery in need of charging is connected across the d. c. terminals of this charger, and consider the result.
Whenever the mid-tap of the transformer secondary is positive with respect to the filament of bulb No. 1, negatrons, which always move toward positive from negative, flow out of the upper end of the secondary to the filament, across the vacuum to the plate, through the fuse and terminal into the negative plate of the battery. From the positive plate of the battery an equal number of negatrons flow through the positive terminal to the resistance unit, and so back to the secondary mid-tap. Thus negatrons are supplied to the negative plate of a storage battery and taken from its positive plate, and the battery, as explained on Page 447, undergoes the electro-chemical process called "charging.''
When the polarity of the transformer secondary reverses itself an open switch appears in this charging circuit, namely, being bulb No. 1, through which the negatrons cannot flow through while the plate of that bulb is negative because a negative plate repels them.
(19) The above is a complete "half -wave" charging or rectifier circuit. It is called a half-wave circuit because charging current flows only half the time, that is, whenever the mid-tap of the secondary winding is positive with respect to the upper end of that secondary. Only half of the a. c. cycle, or wave, is used as charging power.
(20) Now, by tracing the wires, the reader can see for himself that the circuit of bulb No. 2 is exactly the same as the circuit of bulb No. 1, except that it is in reverse polarity. When the mid-tap of the secondary