Speaking arc and singing arc

The talking bow and the singing bow.

The talking bow apparatus consists of a manually adjustable electric arc, a telephone microphone with a small transformer and a switch, an auxiliary microphone battery, and a special induction coil. The arc with its regulator is moved to another room about 15 m away from the telephone. A dark glass filter is used to observe the arc. The arc is ignited by a powerful battery. One of the operators speaks into the microphone, the other adjusts the length of the arc. The voice is weakly reproduced by the electric arc and recorded near it. Telephone currents modulate the direct current of the arc, and its variations produce sounds (not without disturbance). The electric arc can be used as an oscillator in a circuit that also includes a variable capacitor and a coil. The arc is produced in an atmosphere of hydrocarbons (gas beak) which favors the production of electrical oscillations. The frequency of the oscillating circuit is within the audible range. The frequency is changed by changing the capacity of the circuit. By inserting a bundle of iron wires into the coil, we modify its inductance and consequently also the frequency of the circuit.