A CENTURY OF PROGRESS 185
frequencies and long wavelengths,
but with the same overall speed
of propagation—the form of
electromagnetism known today
as radio waves.
Heaviside weighs in
By the time of Hertz’s discovery,
there had been one other important
development that finally produced
Maxwell’s equations in the form
we know today.
In 1884, a British electrical
engineer, mathematician, and
physicist named Oliver
Heaviside—a self-trained genius
who had already patented the
coaxial cable for the efficient
transmission of electrical signals—
devised a way of transforming the
potentials of Maxwell’s equations
into vectors. These were values
that described both the value and
the direction of the force that was
experienced by a charge at a given
point in an electromagnetic field.
By describing the direction of
charges across the field rather than
simply its strength at individual
points, Heaviside reduced a dozen
of the original equations to a mere
four, and in doing so made them
much more useful for practical
applications. Heaviside’s
contribution is largely forgotten
The Maxwell-Heaviside equations,
although couched in the abstruse
mathematical grammar of differential
equations, actually provide a concise
description of the structure and effect
of electrical and magnetic fields.Maxwell’s equations
have had a greater impact
on human history than
any ten presidents.
Carl SaganJames Clerk Maxwell
Born in Edinburgh, Scotland,
in 1831, James Clerk Maxwell
showed genius from an early
age, publishing a scientific
paper on geometry at 14
years old. Educated at the
universities of Edinburgh
and Cambridge, he became a
professor at Marischal College
in Aberdeen, Scotland, at 25
years old. It was there that
he began his work on
electromagnetism.
Maxwell was interested in
many other scientific problems
of the age: in 1859, he was the
first to explain the structure of
Saturn’s rings; between 1855
and 1872, he did important
work on the theory of color
vision, and from 1859 to 1866
he developed a mathematical
model for the distribution of
particle velocities in a gas.
A shy man, Maxwell was
also fond of writing poetry
and remained devoutly
religious all his life. He
died of cancer at 48.Key works1861 On Physical Lines of Force
1864 A Dynamical Theory of
the Electromagnetic Field
1872 Theory of Heat
1873 Treatise on Electricity
and Magnetism∇ ∙ Β = Ο∇ × Ε =‒ —
∂t∂Β∇ × Β = μΟ^ J + μΟεΟ—
∂t∂Ε∇ ∙ Ε = —ρ
εΟtoday, but it is his set of four
elegant equations that now bear
Maxwell’s name.
While Maxwell’s work settled
many questions about the nature
of electricity, magnetism, and
light, it also served to highlight
outstanding mysteries. Perhaps
the most significant of these was
the nature of the medium through
which electromagnetic waves
moved—for surely light waves, like
all others, required such a medium?
The quest to measure this so-called
luminiferous ether was to dominate
physics in the late 19th century,
leading to the development of
some ingenious experiments.
The continued failure to detect
it created a crisis in physics that
would pave the way for the twin
20th-century revolutions of
quantum theory and relativity. ■