HEINRICH HERTZ (1857-1894) Hertz reformulated Maxwell’s equations, thereby demonstrating that electromagnetic waves can travel through free air and vacuum, as established by James Clerk Maxwell and Michael Faraday, Hertz built in his laboratory a transmitter and a receiver of waves. For the transmitter, he used an oscillator, and for the receiver, an antenna as a resonator. Hertz is credited with the classification of electromagnetic spectra. From those perceptible to the human eye and sight, to those not perceptible to the human sense such as infrared rays or ultrasonic sound frequencies.