Radio waves

Long-wave electromagnetic radiation, or radio waves, were discovered by Hertz with the help of a simple detector coil. This validated Maxwell's equations and expanded the known electromagnetic spectrum to include wavelengths far longer than visible light.
 Heinrich Rudolph Hertz Germany 1888 Radio waves

Long-wave electromagnetic radiation, or radio waves, were discovered by Hertz with the help of a simple detector coil. This validated Maxwell's equations and expanded the known electromagnetic spectrum to include wavelengths far longer than visible light.