Heinrich Hertz

German physicist Heinrich Hertz (1857-1894) was the first to verify the predictions of James Clerk Maxwell, made in 1873, regarding the existence of electromagnetic waves. Using a tuned spark gap transmitter and a tuned spark gap detector located a few meters away, he verified in 1887 that electromagnetic waves produced by the transmitter when it sparked caused sparks to appear in the spark gap of the receiver. Hertz also determined that electromagnetic waves could be reflected by metallic objects (the basis of RADAR) and that nonconductors allow the passage of radio waves. He is also credited with the discovery of the photoelectric effect, which is the basis of electronic image transmission.

Hertz' pioneering role has been recognized in the adoption of his name as the electrical unit for the frequency of an electic or electromagnetic wave. A Hertz (Hz) is one cycle per second. A megahertz (mHz) is 1,000,000 cycles per second, and falls right in the middle of the AM radio band.