274
The Body Electric
Everything that runs on a battery produces a DC magnetic field—
from digital watches, cameras, flashlights, and portable radios to
car ignition systems.
Strong magnetic fields are used in industry to refine ore, concen-
trate and recycle scrap iron, purify sewage, soften water for steam
boilers, and many other tasks.
The starting and stopping of an electric train turns the power rail
into a giant antenna that radiates ELF waves for over 100 miles.
Electromagnetic fields vibrating at 60 hertz (50 hertz in Europe
and Russia) surround nearly every person on earth from appliances
at home and machines at work.
Over
500,000
miles
of
high-voltage
power
lines
crisscross
the
United
States.
Innumerable
smaller
lines
feed
into
every
home,
office, factory, and military base, all producing AC or DC fields.
Metal objects near the lines concentrate the fields to higher levels.
In
addition,
high-voltage
lines
are,
in
effect,
gigantic
antennae
operating at 60 hertz in the ELF band, the largest "radio" trans-
mitters
in
the
world.
Switching
stations,
where
the
current
is
changed from one voltage or type to another, emit radio-frequency
waves as well.
AC
magnetic
fields
vibrating
at
100
to
10,000
hertz
emanate
from antitheft systems in stores and libraries, and from metal de-
tectors in airports.
Low-frequency radio waves are used for air and sea navigation,
time references, emergency signals, some amateur radio channels,
and military communications.
Medium frequencies between 535 and 1,604 kilohertz are reserved
for AM radio transmitters, which are limited to 50,000 watts in
this country but are sometimes much more powerful abroad.
HF and VHF channels are filled with chatter from the nation's 35
million CB radios, as well as shortwave bands for more ham ra-
dios, air and sea navigation systems, military uses, spy satellites,
and police and taxi radios. VHF television and FM radio also in-
habit this region. There are now over ten thousand commercial
radio and TV stations in the United States alone, and 7 million
other
radio
transmitters,
not
counting
the
millions
operated
by
the military.
Weather satellites, some kinds of radar, diathermy machines, up-
ward of 10 million microwave ovens, more cop and cab radios,
automatic garage-door openers,
highway emergency call boxes,
and UHF television compete for the low microwave
frequencies.