Invention of Radio - Theory of Electromagnetism

Theory of Electromagnetism

Several scientists speculated that light might be connected with electricity or magnetism. Around 1830 Francesco Zantedeschi suggested a connection between light, electricity, and magnetism.

In 1832 Joseph Henry performed experiments detecting inductive magnetic effects over a distance of 200 feet (61 m) and postulated the existence of electromagnetic waves. He was the first (1838–42) to produce high frequency AC electrical oscillations, and to point out and experimentally demonstrate that the discharge of a condenser under certain conditions is oscillatory, or, as he puts it, consists "of a principal discharge in one direction and then several reflex actions backward and forward, each more feeble than the preceding until equilibrium is attained". This view was also later adopted by Helmholz, but the mathematical demonstration of this fact was first given by Lord Kelvin in his paper on "Transient Electric Currents".

In 1831, Michael Faraday began a series of experiments in which he discovered electromagnetic induction. The relation was mathematically modelled by Faraday's law, which subsequently became one of the four Maxwell equations. Faraday proposed that electromagnetic forces extended into the empty space around the conductor, but did not complete his work involving that proposal. In 1846 Michael Faraday speculated that light was a wave disturbance in a force field".

Between 1861 and 1865, based on the earlier experimental work of Faraday and other scientists, James Clerk Maxwell developed his theory of electromagnetism, which predicted the existence of electromagnetic waves. In 1873 Maxwell described the theoretical basis of the propagation of electromagnetic waves in his paper to the Royal Society, "A Dynamical Theory of the Electromagnetic Field."

Based on the experimental work of Faraday and other physicists, James Clerk Maxwell in 1864 developed the theory of electromagnetism that predicted the existence of electromagnetic waves, which include radio waves. This theory united all previously unrelated observations, experiments and equations of electricity, magnetism, and optics into a consistent theory. His set of equations—Maxwell's equations—demonstrated that electricity, magnetism, and light are all manifestations of the same phenomenon, the electromagnetic field. Subsequently, all other classic laws or equations of these disciplines were special cases of Maxwell's equations. Maxwell's work in electromagnetism has been called the "second great unification in physics".

Although Maxwell did not transmit or receive radio waves his equations still remain the basis of all radio design. Berend Wilhelm Feddersen (German physicist) in 1859, as a private scholar in Leipzig, succeeded in experiments with the Leyden jar to prove that electric sparks were composed of discharge (damped) oscillations. He realized that they arise from a coil, capacitor and resistor existing electrical circuit oscillations.

In 1870 the German physicist Wilhelm von Bezold discovered and demonstrated the fact that the advancing and reflected oscillations produced in conductors by a condenser discharge gave rise to interference phenomena. Professors Elihu Thomson and E. J. Houston in 1876 made a number of experiments and observations on high frequency oscillatory discharges. In 1883 G. F. Fitzgerald suggested at a British Association meeting that electromagnetic waves could be generated by the discharge of a condenser, but the suggestion was not followed up, possibly because no means was known for detecting the waves.