How did Heinrich Hertz demonstrate that radio waves behaved like light?

In the late 1880s, Heinrich Hertz provided the experimental proof needed to validate James Clerk Maxwell’s theory of electromagnetism. By generating electromagnetic waves in his laboratory, Hertz demonstrated that these waves—later known as radio waves—shared the fundamental physical properties of light and heat.123

Hertz’s experimental setup included a spark gap at the center of a parabolic metal mirror to transmit waves, with a wire ring acting as a receiver at the focus of a second collector. Through these experiments, he observed that the waves traveled in straight lines and exhibited the same behaviors as light, including:

• Reflection: Waves could be reflected by metal sheets just as light is reflected by a mirror.13
• Refraction and Diffraction: The waves demonstrated susceptibility to these phenomena, consistent with light waves.23
• Interference: He confirmed that radio waves undergo interference.3
• Polarization: He showed that the waves could be polarized, with electric and magnetic fields oscillating transversely to the direction of motion.3

Additionally, Hertz measured their velocity and confirmed it matched the speed of light, definitively proving that light is a form of electromagnetic radiation.23