A tiny spark across a wire loop made Maxwell's invisible waves visible.
Year
1888
People
Heinrich Hertz, James Clerk Maxwell, Hermann von Helmholtz
Ideas at stake
radio wave, electromagnetic wave, resonance, experiment
Looking for a wave no eye could see
Maxwell’s equations predicted electromagnetic waves, but a prediction on paper was not yet a laboratory object. Heinrich Hertz built a transmitter with a spark gap and a simple receiving loop with another tiny gap.
When the transmitter sparked, a much smaller spark appeared in the receiver across the room. Hertz varied the geometry, reflected the radiation, and formed standing-wave patterns.
Visual motion is compressed to fit the diagram; readouts still use the physical distance.
Playback speed is adjusted; time readouts still show physical time.
The new radiation reflected, refracted, interfered, and polarized like light. Its speed was consistent with the electromagnetic prediction. Light had acquired an invisible family.
Hertz did not foresee radio broadcasting and reportedly doubted practical applications. His apparatus answered a narrower question beautifully: can a changing electric current launch a field disturbance that travels through space?
The answer crossed the room as an invisible wave and announced itself with a spark almost too small to see.
