51
When white light passes through a
prism, it is refracted into its component
parts. Huygens explained that this is
due to light waves traveling at different
speeds through different materials.See also: Alhazen 28–29 ■ Robert Hooke 54 ■ Isaac Newton 62–69 ■ Thomas Young 110–11 ■
James Clerk Maxwell 180–85 ■ Albert Einstein 214–21
SCIENTIFIC REVOLUTION
the “rainbow” effect seen when
light passes through a prism is
produced because the prism has
somehow stained the light. Newton
demonstrated that the “white” light
that we see is actually a mixture of
different colors of light, and these
are split up by a prism because
they are all refracted by slightly
different amounts.
As with many natural
philosophers of the time, Newton
held that light was made up of a
stream of particles, or “corpuscles.”
This idea explained how light
traveled in straight lines and
“bounced” off reflective surfaces. It
also explained refraction in terms of
forces at the boundaries between
different materials.
Partial reflection
However, Newton’s theory could
not explain how, when light hits
many surfaces, some is reflected
and some is refracted. In 1678,
Huygens argued that space was
filled with weightless particles
(the ether), and that light caused
disturbances in the ether that
spread out in spherical waves.
Refraction was thus explained
if different materials (be they ether,
water, or glass) caused light waves
to travel at different speeds.
Huygens’ theory could explain why
both reflection and refraction can
occur at a surface. It could also
explain diffraction.
Huygens’ ideas made little
impact at the time. This was in
part due to Newton’s already giant
stature as a scientist. However, acentury later, in 1803, Thomas
Young showed that light does
indeed behave as a wave, and
experiments in the 20th century
have shown that it behaves both
like a wave and a particle, although
there are big differences between
Huygens’ “spherical waves” and
our modern models of light.
Huygens said that light waves were
longitudinal as they passed through
a substance—the ether. Sound
waves are also longitudinal waves,
in which the particles of the
substance the wave is passing
through vibrate in the same
direction as the wave is traveling.
Our modern view of light waves is
that they are transverse waves that
behave more like waves of water.
They do not need matter to
propagate (transmit), while particles
vibrate at right angles (up and
down) to the wave’s direction. ■Christiaan Huygens Dutch mathematician and
astronomer Christiaan Huygens
was born in The Hague in 1629.
He studied law and mathematics
at his university, then devoted
some time to his own research,
initially in mathematics but then
also in optics, working on
telescopes and grinding his
own lenses.
Huygens visited England
several times, and met Isaac
Newton in 1689. In addition to
his work on light, Huygens had
studied forces and motion, but he
did not accept Newton’s idea of
“action at a distance” to describethe force of gravity. Huygens’
wide-ranging achievements
included some of the most
accurate clocks of his time, the
result of his work on pendulums.
His astronomical work, carried
out using his own telescopes,
included the discovery of Titan,
the largest of Saturn’s moons,
and the first correct description
of Saturn’s rings.Key works1656 De Saturni Luna
Observatio Nova
1690 Treatise on Light