What is light? In the 1860s James Clerk Maxwell used his unified theory of electromagnetism to show that light travelled at the same speed as electromagnetic waves. So were the two phenomena the same thing? It was only two decades later that a series of - literally - brilliant experiments by the German physicist Heinrich Hertz showed that they were. Starting in 1886 at the University of Karlsruhe, Hertz set up an oscillator made of polished brass knobs connected to induction coils. Given a sufficiently high driving voltage, sparks would leap across a gap in the circuit. If light and electromagnetic waves were the same thing, waves would be generated every time a spark appeared and be registered by the induction coil. And so they were.
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