German physicist who experimentally proved the existence of electromagnetic waves in 1888. His apparatus consisted of a wire connected to an induction coil to produce the waves and a small loop of wire with a spark gap to detect them. When currents were induced in the detection loop, the induced current produced a spark across the gap. With further experiments involving mirrors, prisms, and metal gratings, he showed his electromagnetic waves to have analogous properties as light. In the process of his investigation, he discovered but did not recognize the photoelectric effect.

In another important contribution, he reformulated Maxwell's complicated field equations into a symmetric and compact form in Untersuchungen über die Ausbereitung der elektrischen Kraft (Investigations on the Propagation of Electric Force) (1892). He criticized Maxwell's definition of electric charge and concept of displacement current, which he replaced with a mathematical formalism. Hertz's simplification of Maxwell's theory to a mathematical formalism led to its widespread acceptance.