What is the Electromagnetic Spectrum?
The first region other than the section of the spectrum visible to human eyes was the infrared portion. William Herschel, also known as the discoverer of the first planet to be revealed in modern times, Uranus, was responsible for slowing rays of light with a prism, and redirecting the light rays into heat-absorbing bulbs. He found that the “caloric rays” were most intense beyond the red portion, producing the highest absorption temperatures yet the rays could be refracted and reflected like visible light.
In Germany, Johann Ritter, learning about Herschel’s discovery, attempted to identify the complementary radiation beyond the violet region of the visible spectrum by exposing silver chloride crystals to refracted sunlight. Ritter originally called this new discovery “chemical radiation” but in time, this radiation became known as ultraviolet (beyond the violet).
The next portion of the electromagnetic spectrum to be identified was located in the low energy region. In 1887, German physicist Heinrich Hertz added very long wavelength radio waves to the spectrum, but his research did not pursue applications of this technology as he felt that there was no practical use for it. It was left to Nicola Tesla and Guglielmo Marconi to find ways to utilize “wireless telegraphy” for the public.
The discovery of X-rays followed soon thereafter. Wilhelm Roentgen, a Bavarian physicist, studied the passage of cathode rays from an induction coil through a glass tube that had been partially evacuated. He noticed that these rays when projected upon a fluorescent screen caused it to glow. Roentgen also found that these rays penetrated skin and could cast an image of the bones within upon on photographic plate. The first X-ray image published was that of Frau Roentgen’s hand.
Interest in uncovering new elements and new phenomena such as X-rays was all consuming as the end of the nineteenth century approached. Henri Becquerel, in Paris, discovered that uranium salts were the source of radioactivity. Another Parisian researcher, Paul Villard, also studied radioactive sources and in 1900, established that certain radioactive materials emitted what become known as gamma rays, high-energy radiation with even shorter wavelengths than X-rays.
New applications are continually being added to the complement of uses for the different ranges of wavelengths and frequencies encompassed by the electromagnetic radiation, shedding “light” on previously unexplored areas of potential technology.