Introduction
In 1873, on the basis of a mathematical analysis, English physicist James Clerk Maxwell concluded that light was a propagating wave composed of electricity and magnetism. Some of Maxwell's contemporaries rejected his theory because it seemed to predict too much-an infinite number of non-light waves, none of which had ever been detected. But other scientists began searching for the invisible waves and in 1888 Heinrich Hertz, a German physicist, succeeded. Using what today would be called a transmitter and a receiver, he proved the existence of electromagnetic waves having a frequency of 30 MHz.
Hertz died in 1894 and Guliermo Marconi, then only twenty, read his obituary in an Italian electrical journal. It seemed to Marconi that Hertzian waves had a vast potential in the field of communications; by 1896 he had repeated Hertz's experiments, but with the receiver more than two miles away, not just on the other side of the room. Many successes followed, leading directly to the development of radio in 1910.
In 1922, while accepting the Medal of Honor of the American Institute of Radio Engineers, Marconi said:
In some of my tests, I have noticed the effects of reflection and deflection of [electromagnetic] waves by metallic objects miles away. It seems to me that it should be possible to design apparatus by means of which a ship could radiate or project a divergent beam of these rays in any desired direction, which rays, if coming across a metallic object, such as a ship, would be reflected back to a receiver and thereby immediately reveal the presence and bearing of ships.
Marconi's vision-radar-became a reality in the 1930's, and following World War II many other practical uses for electromagnetic waves were developed.
Paralleling these developments was the birth and growth of the electrical power industry. From a modest beginning in New York City in 1882. under the guidance of Thomas Edison, the industry began the systematic electrification that resulted in a steady increase in power-line construction and in the proliferation of the devices and appliances which they served.
The passage of electricity from a scientific curiosity to a role of major importance in society (Table 10.1) resulted in a profound alteration in the earth's electromagnetic environment. From the origin of life on earth to the beginning of the twentieth century this environment was determined by the sun and other cosmic sources, and by the geomagnetic properties of the earth itself; the intensity was extremely small even by the standards of today's ultrasensitive instrumentation. But by the beginning of the last half of the twentieth century, man-made EMFs were the overwhelmingly dominant constituent of the earth's electromagnetic environment. With the benefit of hindsight, we can now see that it was dangerous to have made such a drastic alteration in our environment without first studying its potential biological impact. But the fact is that the only immediately obvious effects of electricity are shock and heating, and no experimental study before about 1960 and no theoretical study before about 1970 seriously suggested otherwise. It is therefore not surprising that, from a public health standpoint, the best that can be said of the present artificial EMF levels in the environment in the U.S. is that they do not cause shock or heating. Unfortunately, there may be public health consequences of environmental EMFs that are not obvious and which, therefore, are not protected against by the unofficial U.S. EMF exposure limit of 10,000 µW/cm2.
Table 10.1 SOME USES OF EMFs
Typical levels of artificial EMFs in the environment, their consequences, and the basis for our conclusion that they may constitute a public health risk are described below.