In the 1886 Hertz experiment, what did sparks across a gap prove about James Clerk Maxwell’s theory?

Heinrich Hertz’s 1886–1888 experiments showed that electromagnetic waves exist, confirming a key prediction of James Clerk Maxwell’s theory.

Hertz used an oscillating electrical circuit to create rapid electromagnetic disturbances and a separate metal loop with a small gap to detect them. Tiny sparks jumped across the detector gap when the transmitter operated. By studying reflection, refraction, interference, and polarization, Hertz demonstrated that the disturbances behaved like waves and traveled through space.

Maxwell had predicted electromagnetic waves mathematically in the 1860s and had calculated that their speed should match the speed of light. Hertz’s laboratory work supplied direct experimental evidence for that prediction.

Hertz did not discover radio broadcasting as a practical communications industry. His apparatus generated and detected radio-frequency waves, but later engineers, including Guglielmo Marconi, developed long-distance wireless communication systems.