In 1888, in a corner of his physics classroom at the Karlsruhe Polytechnic in Berlin, Hertz generated electric waves by means of the oscillatory discharge of a condenser through a loop provided with a spark gap, and then detecting them with a similar type of circuit. Hertz's condenser was a pair of metal rods, placed end to end with a small gap for a spark between them. When these rods were given charges of opposite signs, strong enough to spark, the current would oscillate back and forth across the gap and along the rods. With this oscillator, Hertz solved two problems: 1) timing Maxwell's waves (he had demonstrated, in the concrete, what Maxwell had only theorized: that the velocity of radio waves was equal to the velocity of light), and 2) how to make the electric and magnetic fields detach themselves from wires and go free as Maxwell's waves.
Hertz's students were impressed, and wondered what use might be made of this marvelous phenomenon. But Hertz thought his discoveries were no more practical than Maxwell's. "It's of no use whatsoever," he replied. "This is just an experiment that proves Maestro Maxwell was right -- we just have these mysterious electromagnetic waves that we cannot see with the naked eye. But they are there."