Maxwell's Silver Hammer 273
gies without instruments, so most people don't realize how drastically
and abruptly we've changed the electromagnetic environment in just one
century. Working at Cambridge University, Scottish physicist James
Clerk Maxwell showed mathematically in 1873 that light was but a
small part of the vast undiscovered realm of radiation. Heinrich Hertz
first found some of the radio waves in 1888. Meanwhile, Edison had set
up the first commercial electric-power system in New York in 1882.
For billions of years before then, the energies that life grew up among
were relatively simple. There was a weak electromagnetic field modulated
by micropulsations within it and further sculpted by the solar and lunar
cycles. There was a burst of static centered at 10,000 hertz and reverberat-
ing over the whole earth whenever lightning flashed in the scores of
thunderstorms in progress at any one time. There were a few weak radio
waves from the sun and other stars. Light, including some infrared and
ultraviolet, was the most abundant form of electromagnetic energy. At
higher frequencies, living things absorbed only small amounts of ionizing
X rays and gamma rays from space and from radioactive minerals in rocks.
Large parts of the energy spectrum were totally silent.
We'll never experience that quiet world again. In 1893 Nikola Tesla
lit the Chicago World's Fair with the first AC power system, and two
years later he began the modern era of electrical engineering by harness-
ing Niagara Falls. In 1901 Guglielmo Marconi sent a radiotelegraph
message across the Atlantic, using without acknowledgment a machine
designed by the prolific Tesla. The invention of the vacuum tube in
1907 led to the first voice transmission by radio in 1915 and the first
commercial station in 1920. Until then many people still ate supper by
candle or kerosene, and the ambient forces remained a reasonable fac-
simile of earth's pristine field.
The greatest changes have all come in the one generation since World
War II. The trend toward use of shorter and shorter radio waves, bounced
off the ionosphere for long-distance communication, had begun before the
war. The fight for survival against fascism impelled the development of
microwave radar, which helped win the Battle of Britain, allowed all-
weather bombing of Germany, and gave the American Navy a decisive
edge over the Japanese. The conflict also produced other electronic devices
of all types. In 1947 Bell Telephone set up the first microwave phone relay
towers between New York and Boston, the same year the first commercial
television broadcasts, also transmitted by microwaves, began. Since then
nearly every human involved an electrical appliance, and today
we're all awash in a sea of energies life has never before experienced, of
which the following list of sources only skims the surface: