Posted on June 4, 2008
One difficulty with writing about this topic is that it is not completely clear just what “radio” is. If by Radio is meant (as my dictionary says) “The transmission and reception of electromagnetic waves without a connecting wire,” then Radio existed since prehistoric times. Light is composed of electromagnetic waves, and signaling by light is as old as Man himself. Interestingly, the IEEE Standard Dictionary does not have a definition of Radio as a noun, but uses the word as an adjective, such as in “radio frequency,” or “radio receiver.” The definition of a Radio Receiver is “a device for converting radio frequency power into receptible signals.” and Radio Frequency is “a frequency in the electomagnetic spectrum that is between the audio frequency portion and the infrared portion.” So, since radio is below infrared in frequency, light (or ultaviolet, x-rays, or cosmic rays, etc.) is not radio.
One aspect of the definition of Radio that is not mentioned by either Webster’s or the IEEE is that it has historically been differentiated from induction, which is the transission of electromagnetic energy from one circuit to another. The only thing that differentiates induction from radio is that radio involves propagating waves, while the waves that produce induction do not propagate. The boundary between induction and radiation is a half wavelength from the radiator.
As is well-known, radio started with the production of electrical sparks. Indeed, a common nickname that had been given to radio operators was “Sparks.” Sparks are produced naturally by lightning, and humans have made and used devices for making electric sparks since ancient times. The devices that produce sparks were early radio transmitters. Without a tuning circuit, the sparks produce incoherent radiation over a very wide bandwidth.
So, radio transmitters have existed for millenia, but radio receivers have been developed much more recently. In 1842, American scientist Joseph Henry (in whose honor the unit of inductance was named) observed that “induction” caused by a spark produced by the discharge of a capacitor (specifically, a Leyden jar) could be detected over a long distance.
I think, however, that the first experimental observation of radio signals was made by Luigi Galvani, a professor of anatomy, who, in 1780, discovered by accident that when a nerve of a freshly dissected frog was touched by a scalpel, and an electric machine some distance away produced a spark, the limbs of the frog twitched. The electric machine was the transmitter in this radio system, the scalpel was the receiving antenna, and the frog was a sensitive electrical detector.
Galvani and his followers completely misunderstood this discovery, and it led to a long detour in electrical science. Some thought that electricity can be used to “restore life.” An extreme example of this misunderstanding is the very bad novel, “Frankenstein,” written by the bright, but silly, eighteen-year old Mary Wollstonecraft Godwin (a.k.a. Mary Shelley, because she became the second wife of the famous poet, Percy Bisshe Shelley) in 1816. Fortunately, Mary’s bad novel was made into a pretty good movie more than a century later. As the movie shows very dramatically, electricity was used to restore life to the monster. A good result of galvanism is that it was the beginning of neuroscience, and it also led to several other electrical discoveries once the nonsense was cleared up. A bad result of galvanism is that it started medical quackery involving useless electrical devices, and this persists even to this day.
Radio, as we understand it today, began in 1868 when Maxwell published his electromagnetic theory of light. Maxwell proved the existence of electromagnetic waves mathematically, and he supposed that light consisted of electromagnetic waves. His theory was not immediately accepted by everybody, because a competing theory of electomagnetism by Weber did not show the existence of electromagnetic waves, and assumed that all electromagnetic interactions were instantaneous, without any delay because of the finite speed of light. So, it remained to be proved by experiment that electromagnetic waves existed.
In 1883, Fitzgerald (The same man who discovered the “Fitzgerald Contraction” in the Theory of Relativity) proposed what he called a “magnetic oscillator” for generating radio waves. The radiator was to be a loop antenna tuned by a capacitor. Not being much of an engineer, Fitzgerald was not able to supply many details about how to construct this device. In his experiments in 1887 and 1888, Hertz constructed an oscillator, not unlike Fitzgerald’s, but having a dipole antenna and a tuning coil. He demonstrated that the velocity of the waves was finite, and about the speed of light. He also showed that electromagnetic waves, like light, have reflection and refraction. So, Maxwell’s theory was proved.
The story of early radio would not be complete if the experiments of one David Edward Hughes were not related. He told his sad tale in an 1899 edition of “The Electrician.” In 1880, Hughes demonstrated the transmission of electromagnetic waves over a distance of five hundred yards. A very distiguished audience witnessed the demonstration. There was the President of the Royal Society, the chief electrical engineer of the British Post Office, and, most importantly, Sir George Gabriel Stokes. Stokes is a very important name in hydrodynamics. There are the Navier-Stokes equations, the concept of Stokes Flow, and the Stokes-Einstein equation. Less-known is his work on fundamental electrical theory during the middle of the nineteenth century, and his theories of the “ether.” This distinguished panel of observers concluded that the phenomenon of Hughes’s demonstration was probably merely induction, and not evidence of electromagnetic waves.
As I have experienced myself, it does little good to have great men judge your work. If they do not consider you to be their peer, they will not look favorably upon your views. I have reported on something like this in recent posts in the part15.us Forum.