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People Behind the Science

James Clerk Maxwell (1831–1879)

ames Maxwell was a British physicist who the electromagnetic field. These showed
Jdiscovered that light consists of electro- that light is propagated in two waves, one
magnetic waves and established the kinetic magnetic and the other electric, which
theory of gases. He also proved the nature vibrate perpendicular to each other and
of Saturn’s rings and demonstrated the prin- to the direction of propagation. This
ciples governing color vision. was confirmed in Maxwell’s Note on the
Maxwell was born in Edinburgh, Electromagnetic Theory of Light (1868),
Scotland, on November 13, 1831. He was which used an electrical derivation of the
educated at Edinburgh Academy from 1841 theory instead of the dynamical formula-
to 1847, and then he entered the University tion, and Maxwell’s whole work on the
of Edinburgh. He next entered Cambridge subject was summed up in Treatise on Elec-
University in 1850, graduating in 1854. He tricity and Magnetism in 1873.
became professor of natural philosophy at The treatise also established that light
Marischal College, Aberdeen, in 1856 and has a radiation pressure and suggested that a
moved to London in 1860 to take up the whole family of electromagnetic radiations
post of professor of natural philosophy and must exist, of which light was only one. This
astronomy at King’s College. On the death was confirmed in 1888 with the sensational
of his father in 1865, Maxwell returned to discovery of radio waves by Heinrich Hertz
his family home in Scotland and devoted (1857–1894). Sadly, Maxwell did not live
himself to research. However, in 1871, he long enough to see this triumphant vindica-
was persuaded to move to Cambridge, tion of his work.
where he became the first professor of Maxwell is generally considered to
experimental physics and set up the Cav- be the greatest theoretical physicist of the
endish Laboratory, which opened in 1874. the behavior of the lines of force and the 1800s, as his forebear Faraday was the
Maxwell continued in this position until flow of an incompressible liquid, thereby greatest experimental physicist. His rigor-
1879, when he contracted cancer. He died deriving equations that represented known ous mathematical ability was combined
in Cambridge on November 5, 1879, at the electric and magnetic effects. The next step with great insight to enable him to achieve
age of 48. toward the electromagnetic theory took brilliant syntheses of knowledge in the two
Maxwell’s development of the electro- place with the publication of the paper “On most important areas of physics at that
magnetic theory of light took many years. It Physical Lines of Force” (1861 –1862). In time. In building on Faraday’s work to dis-
began with the paper “On Faraday’s Lines of it, Maxwell developed a model for the cover the electromagnetic nature of light,
Force,” in which Maxwell built on the views medium in which electric and magnetic Maxwell not only explained electromagne-
of Michael Faraday (1791–1867) that elec- effects could occur. tism but also paved the way for the discov-
tric and magnetic effects result from fields of In A Dynamical Theory of the Electro- ery and application of the whole spectrum
lines of force that surround conductors and magnetic Field (1864), Maxwell developed of electro magnetic radiation that has char-
magnets. Maxwell drew an analogy between the fundamental equations that describe acterized modern physics.

Source: Modified from the Hutchinson Dictionary of Scientific Biography © Research Machines 2008. All rights reserved. Helicon Publishing is a division of Research Machines.

The special theory of relativity is based solely on the consis-

tent law principle and the constancy of speed principle. Together, GENERAL THEORY
these principles result in some very interesting outcomes if you Einstein’s general theory of relativity could also be called Ein-
compare measurements from the ground of the length, time, and stein’s geometric theory of gravity. According to Einstein, a
mass of a very fast airplane with measurements made by someone gravitational interaction does not come from some mysterious
moving with the airplane. You, on the ground, would fi nd that force called gravity. Instead, the interaction is between a mass
and the geometry of space and time where the mass is located.
• The length of an object is shorter when it is moving.
Space and time can be combined into a fourth-dimensional
• Moving clocks run more slowly.
“spacetime” structure. A mass is understood to interact with
• Moving objects have increased mass.
the spacetime, telling it how to curve. Space-time also interacts

The special theory of relativity shows that measurements of with a mass, telling it how to move. A gravitational interaction

length, time, and mass are different in different moving reference is considered to be a local event of movement along a geodesic

frames. Einstein developed equations that describe each of the (shortest distance between two points on a curved surface) in
changes described above. These changes have been verifi ed curved spacetime (Figure 7.26). Th is different viewpoint has led

countless times with elementary particle experiments, and the to much more accurate measurements and has been tested by

data always fit Einstein’s equations with predicted results. many events in astronomy (see p. 388 for one example).
7-21 CHAPTER 7 Light 197