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Who discovered radio?

How do we know that electricity, magnetism and light are all part of one electromagnetic spectrum, and can be considered as travelling in waves? 
It is mainly due to the work of scientists in the 19th century, whose discoveries became the basis for the invention of practical radio sets.

The fruitful year of 1831

In 1802, Gian Domenico Romagnosi was the first to publish the suggestion that electricity and magnetism are related. In 1820, Hans Christian ěrsted found that an electric current produces a magnetic field as it flows through a wire. In the 1830s, American scientist Joseph Henry wound wire around iron cores to make electromagnets and experimented with using electricity to induce magnetism remotely. He was working at about the same time as Michael  Faraday (1791–1867), the British scientist who described the phenomenon of electromagnetic induction in 1831.

Did David Edward Hughes use radio to receive the world’s first mobile phone call?

Induction occurs when an electric field is produced by a changing magnetic field, or vice versa. Faraday also established that magnetism can affect rays of light, demonstrating the relationship between the two phenomena. Importantly, he suggested that lines of electromagnetic force extend from charged bodies into their surroundings — an essential concept on the way to radio. In the year that Faraday formulated his law of induction, a Scottish physicist was born who consolidated it into a set of mathematical laws on electromagnetism: James Clerk Maxwell (1831–1879).

Albert Einstein described Maxwell’s work as "the most profound and the most fruitful that physics has experienced since the time of Newton". In 1864, he incorporated Faraday’s law into a comprehensive model known as Maxwell’s Equations. These predicted that electric and magnetic fields travel through space in waves at the speed of light. Maxwell concluded that light is indeed an electromagnetic wave, and said that other types of phenomena at different wavelengths should also exist. In other words, he predicted the existence of radio.

But who first observed radio waves in reality? A number of investigators noticed "electricity at a distance" including Thomas Alva Edison, who in 1875 said he had encountered "aetheric force" while working on telegraphy. But to answer the question posed in the previous Pioneers’ Page, it was another scientist born in Britain in 1831, David Edward Hughes, who was the first person to definitely record sending and receiving a radio signal.

Microphone and "mobile phone"

Hughes (1831–1900) was best known for his inventions in telegraphy (see Pioneers’ Page for July/August 2007). In 1876 the telephone was invented and, like others, Hughes began experiments to improve its transmission of sound. His system comprised a tube containing two carbon rods in loose contact, included in an electrical circuit with a battery. When the tube was subjected to sound vibrations, the electrical resistance varied to match the sound waves’ form. In 1878, Hughes announced his invention, which he called a "microphone".

Continuing his research, Hughes discovered that the carbon-filled tubes were also sensitive to "sudden electric impulses". To test at what distance this effect could act, Hughes set up a source of regular electric sparks in his house and then walked out into the street carrying a tube in circuit with a battery and a telephone. He found that, as the sparks were generated, he could hear corresponding clicks in the telephone from up to 500 yards (457 metres) away. It was not a modulated signal — let alone words — that he heard; however, in a sense, in 1878 Hughes had received the world’s first mobile phone call.

Hughes suggested that this wireless transmission of signals in the super low frequency range was accomplished through "electric waves" that could travel through buildings and the air. He demonstrated his results to the Royal Society in 1880, but they were considered to be due to induction rather than electricity acting at a distance. He finally received credit for his work many years later, after a sound experimental framework for radio had been laid by the German scientist Heinrich Rudolf Hertz (1857–1894).

Action at a distance

Heinrich Rudolf Hertz established the experimental framework for radio

Hertz validated Maxwell’s theory through experimentally proving the existence of electromagnetic waves. He confirmed that light is a form of radiation and, using a spark-gap transmitter, in 1888 produced ultra high frequency (UHF) radio waves at around 100 MHz in the shortwave band. He also found that radio waves could be transmitted through, or stopped by, various materials and could be focused by parabolic reflectors. "Action at a distance is for the first time proved," said Hertz in the 1893 English edition of his work (published in German in 1891). "Electric forces can disentangle themselves from material bodies, and can continue to subsist as conditions or changes in the state of space."

We now measure radio frequencies in a unit called "Hertz". But despite the triumph of his research, the scientist did not envisage any useful applications of his experiments. He died at the early age of 37 at about the same time that such figures as Tesla, Popov and Marconi began work that led to practical radio systems — more than a decade after Hughes’s original observations.


Question for next time

Who was "the man who brought silicon to
Silicon Valley"?




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