The Dynamophone

A sentence linking human “muscular forces” to “mechanical effects” in a metaphor that isn’t signaled as such becomes possible thanks to the rise of the “human motor” as a dominant form of political, social, technical and scientific thought from the late nineteenth century through the interwar period. Anson Rabinbach has shown how labor is transformed into “labor power” over this period, “a concept emphasizing the expenditure and deployment of energy as opposed to human will, moral purpose, or even technical skill.” Predicated on a utopian ideal of a body without fatigue, discourse on the human motor sought to marry the motion of the body with that of the machine:

European scientists devised sophisticated techniques to measure the expenditure of mental and physical energy during mechanical work—not only of the worker, but also of the student, and even of the philosopher. If the working body was a motor, some scientists reasoned, it might even be possible to eliminate the stubborn resistance to perpetual work that distinguished the human body from a machine. If fatigue, the endemic disorder of industrial society, could be analyzed and overcome, the last obstacle to progress would be eliminated.

@rabinbach_human_1992, 2. ↩

This is the problem that first led Reginald Fessenden to discover the heterodyne principle in 1901: two electrical waves of different frequencies can amplify one another, even to the point of producing frequencies in the audible range. Hugh Aitken: “The word [heterodyne], now part of every radio engineer’s vocabulary, was Fessenden’s coinage, reflecting his early training in Greek: to heterodyne meant to mix two different forces—in this case, two waves of different frequency.” Fessenden was exploring the question of why early detectors like the liquid barretter couldn’t produce a signal powerful enough to produce sound through a telephone earpiece, or “move the diaphragm … at audio frequencies.”

Fessenden’s answer was to feed two currents into the earpiece: one the antenna current, a train of oscillations at the signal frequency, and the other a train of oscillations generated either locally at the receiver or at a second transmitter, with the two frequencies differing slightly from each other. The two frequencies would mix or ‘beat’ against each other, and if the difference between them were correctly chosen, the result would be a wave train that the metal diaphragm of the earpiece could follow and that the human ear could hear.

Much like the sympathetic vibrations of a piano tuner or undamped guitar strings, these two currents resonate with one another. @aitken_continuous_1985, 58. ↩

The coherer is one of the earliest forms of “detector” and the most important component of a wireless set. The detector is responsible for demodulating radio frequency signals into an audio frequency current, ready to be piped through the listener’s headphones. The idea behind the coherer is that when a radio frequency signal is applied to a glass vial filled with metal powder, the metal filings will “cohere” and an electrical current will pass through the device. Each telegraphic “dot” or “dash” causes the filings to cohere, after which some form of “decoherer” mechanically taps the vial to loosen them once again.

The coherer was initially discovered by the physicist and inventor Édouard Branly (1844 – 1940). A 1904 article written by wireless pioneer Lee De Forest explains, “The form and nature of the ordinary filings-tube coherer, as applied to-day in wireless telegraphy, is fairly familiar. Branley [sic] discovered, in 1891, that the effect of electrical oscillations upon a body of metal fillings was to produce a marked increase in the conductivity of the mass, a conductivity which persisted until the particles were broken apart again by mechanical jar.” @de_forest_electrolytic_1904, p. 424.

It was left for Marconi to, in the words of electrical engineer Thomas H. Lee, combine Hertz’s spark-gap transmitter with Branly’s coherer and “tinker like crazy” to produce the first wireless telegraph set. It is worth noting that the physical principle behind the coherer’s operation is still not understood today. It remains a device with practical applications whose inner workings are nevertheless not understood. @lee_nonlinear_2004, p. 3. ↩

The Telimco—a portmanteau of “The Electro Importing Company” and their flagship product—was the first fully-assembled radio set ever sold to the American public, with transmitting and receiving models made available. For the Dynamophone described here, picture a Telimco transmitter retrofitted with a telephone mouthpiece, and a Telimco receiver hooked up to some form of motor. As long as the user speaks into that mouthpiece on the transmitter, the motor on the receiving end would run.

Blueprints for such jury rigged apparatuses were typical of Modern Electrics at the time, and were presented as if they were easily replicable by readers who could stock their home workshops with parts from the Electro Importing Catalog. This issue, for instance, also contains instructions by Gernsback for building an alarm clock (“An Electric Sun Alarm”) connected to light-sensitive selenium cells (used in early television prototypes – see Television and the Telephot) that would set the alarm ringing when hit by the morning sunlight.

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Though the coherer wasn’t as sensitive as later crystal and electrolytic detectors, it had the merit of being the only one to work in mobile applications until the late 1910s. In a later editorial on what he refers to as “radio kinetics,” Gernsback writes of the shortcomings and unique benefits of the coherer:

as far back as 1906 this investigator fired guns, closed doors, started and stopt motors by means of distant radio control. This was in the age of the coherer, and probably due to its inherent shortcomings, the art of radio kinetics was not much advanced until very recently. The coherer is a very unsatisfactory scientific instrument insofar that even if constructed by precision mechanics, it has the great inherent fault of being susceptible to shocks as well as to most extraneous impulses. Thus, for instance, a very sensitive coherer will usually operate on strays or static as well as inductive effects and stray waves. In other words this instrument—even the most balanced one—is not reliable. It will go off when least expected. A coherer heretofore was thought to be the prime necessity for radio kinetics because it was practically the only instrument known that could close the contacts of a relay. Ordinary detectors such as the crystal type and others could not be used until about three or four years ago, at which time very sensitive galvanometer relays were introduced which actually could be used to close a contact by means of a carborundum or silicon detector.”

@gernsback_radio_1920. ↩

This issue of Modern Electrics contained the first winner of a regular “Laboratory Contest” section. Reader Irving Kimball impressed with the submission of his “vitaphone,” a device that combined motion picture and sound reproduction. “The original model of his motor-pyrograph,’ an automated electrically operated pyrograph or wood-burning machine, works to perfection.” (63) ↩