Deutsch
Singing Arc
Daniel Gethmann
The Usefulness of Negative Resistance
The singing arc was presented by the British physicist William Duddell (1872–1917) to the London Institution of Electrical Engineers on 13 December 1900. The special switching of the arc so as to play music – Duddell played the national anthem to demonstrate the arc – also gave it the name “musical arc.” The inventor was a skilful designer of physical experimental apparatus at the London Central Technical College, examining in particular the effects of the electric arc. The singing arc was, in the context of his research in physics, initially an ingenious and spectacular laboratory effect that embodied the idea of electronic sound production and musical synthesis in an early apparatus. That a physics experimental apparatus began a new chapter in music instrument making should not however distract from the central research issue of this interlacing of physics and music, namely whether and how an arc can be used to transmit voices, music and noises across the ether.
The natural scientist Humphry Davy was the first to report on the electric arc after generating a low DC voltage with a high amperage between two carbons using the battery recently invented by Alessandro Volta. The arcs thus created were used as early electric street lighting, so bright that they were used in both world wars in anti-aircraft searchlights. Long before Heinrich Hertz’s experiments to prove the existence of electromagnetic waves (1886–1888), it had been noticed in arc discharges that the voltage temporarily fell as the amperage increased. The mathematician Hertha Ayrton, who continued the research work of her husband William Ayrton on the electric arc, set out the formula on the inverse proportionality between arc amperage and voltage known as “negative resistance.” She was the first woman to be made a member of the Institution of Electrical Engineers in recognition of her research.
Her discoveries were taken over by the physicist George Francis Fitzgerald to support his thesis that the negative resistance of the arc could be used to produce unsuppressed continuous electromagnetic waves, since this resistance to some extent overcame the resistance of the second circuit. William Duddell, a colleague of Hertha and William Ayrton at the London Central Technical College, then discovered that the arc of a DC arc lamp begins to “sing” without any further conversion if an oscillating circuit is switched in parallel to it. The physicist Hermann Theodor Simon having already connected the arc as a loudspeaker to a telephone, thereby inventing the “talking arc,” Duddell accidentally discovered its musical characteristics. Using the oscillograph he had previously invented, he adjusted the circuit to the calculated values of notes, and the addition of a keyboard made the circuit into a musical instrument.
Despite further experiments, Duddell was unable to generate electromagnetic waves with the singing arc, since the negative resistance disappears at higher frequencies. Finally, the Danish physicists Valdemar Poulsen and P. O. Pedersen followed up Duddell’s work and in 1902 patented an arc transmitter that generated unsuppressed oscillations, thereby permitting radio transmission of song and music from 1906 on. Thus the singing arc embodied both the idea of a purely electronic sound machine and a clear concept of a technology for broadcasting musical events.