A CENTURY OF PROGRESS 183
in a single direction, easily created
by bouncing a beam of light off a
smooth reflecting surface) through
a strong magnetic field, and testing
the angle of polarization on the
other side using a special eyepiece.
He found that by rotating the
orientation of the magnetic field,
he was able to affect the angle of
polarization of the light. Based on
this discovery, Faraday argued for
the first time that light waves were
some kind of undulation in the lines
of force by which he interpreted
electromagnetic phenomena.
Theories of
electromagnetism
However, while Faraday was
a brilliant experimentalist, it
took the genius of Maxwell to put
this intuitive idea onto sound
theoretical footing. Maxwell came
to the problem from the opposite
direction, discovering the link
between electricity, magnetism,
and light almost by accident.
Maxwell’s main concern
was to explain just how the
electromagnetic forces involved
in phenomena such as Faraday’s
induction—where a moving
magnet induces an electric
current—were operating. Faraday
had invented the ingenious idea
of “lines of force," spreading in
concentric rings around moving
electric currents, or emerging and
reentering the poles of magnets.
When electrical conductors moved
in relation to these lines, currents
flowed within them. The density of
the lines of force and the speed of
relative motion both influenced the
strength of the current.
But while lines of force were
a useful aid to understanding
the phenomenon, they did not have
a physical existence—electrical
and magnetic fields make theirSee also: Alessandro Volta 90–95 ■ Hans Christian Ørsted 120 ■ Michael Faraday 121 ■ Max Planck 202–05 ■
Albert Einstein 214–21 ■ Richard Feynman 272–73 ■ Sheldon Glashow 292–93
presence felt at every point in
space that lies within their range
of influence, not just when certain
lines are cut. Scientists who
attempted to describe the physics
of electromagnetism tended to fall
into one of two schools: those who
saw electromagnetism as some
form of “action at a distance”
similar to Newton’s model of
gravity, and those who believed
that electromagnetism was
propagated through space by
waves. In general, the supporters
of “action at a distance” hailed from
continental Europe and followed
the theories of electrical pioneer
André-Marie Ampère (p.120), while
the believers in waves tended
to be British. One clear way of
distinguishing between the two
basic theories was that action
at a distance would take place
instantaneously, while waves
would inevitably take some time
to propagate through space. ❯❯The special theory of relativity
owes its origins to Maxwell’s
equations of the
electromagnetic field.
Albert EinsteinThe pattern of iron filings around
a magnet would seem to suggest the
lines of force described by Faraday. In
fact they show the direction of the force
experienced by a charge at a given
point in an electromagentic field, as
represented in Maxwell's equations.