There was major scientific interest in electricity
throughout the eighteenth and nineteenth centuries, and much progress
was made. During the 1700's interest focused on static
electricity, and the science consisted mostly of various experiments
with electrical phenomena followed by qualitative theories attempting to
explain the results. but in 1800, the invention of the battery by
Allesandro Volta sparked a new
electrical revolution, marked by a new generation of quantitative
scientists such as André-Marie Ampère ,
Joseph Henry, Georg
Ohm, and Michael Faraday.
Faraday was the first to propose the concept of an
electromagnetic field - lines of force which spread out in all
directions to fill space, and to affect matter within that space.15
It was James Clerk Maxwell,
however, who built the theoretical bridge from electricity to radio.
Intrigued by Faraday's work, Maxwell developed a set of equations
to describe mathematically how a changing magnetic field produced
an electric field (electrical induction). He discovered that the
opposite was also true, and that changing magnetic and electric fields
in space produced electromagnetic waves. He showed how these waves
traveled at the speed of light, and that in fact, light was just another
form of electromagnetic wave. Maxwell presented his analysis in 1873, in
the two volume books entitled "A Treatise on
Electricity and Magnetism."
Little progress toward radio was made until 6 years later when the
Prussian Academy of science offered an award to "establish
experimentally any relationship between electromagnetic forces and the
dielectric polarization of insulators." A bright young professor of
physics at the Engineering College in Karlsruhe, Germany, named
Hertz picked up the challenge and began a series of experiments.
Two pieces similar to the apparatus Hertz used are shown in Figures 1
and 2 below. The Spark gap in figure 1 was connected to an
induction coil. The "resonator" (Fig. 2) was placed on a bench
nearby. During the course of his work, Hertz noticed that when the
induction coil was activated, a small spark appeared in the resonator.
Since the resonator had no physical connection to the induction coil or
spark gap Hertz knew he was witnessing a new phenomenon.
Hertz thus confirmed Maxwell's theory. Through a series of ingenious
experiments he went on to confirm that this new phenomena were indeed
waves, they traveled at the speed of light, and that the waves could be
reflected, refracted and polarized, the same as light waves. He was also
able to calculate their wavelength and frequency.
Hertz's discovery led to a groundswell of interest by many people,
including a young Italian named Guglielmo Marconi.