Hertzian Wave Detector
   Physicists had been generating electromagnetic waves from the first time that a discharge between two conductors took place. The system's inherent capacitance and inductance controlled the frequency of the resulting propagated electromagnetic disturbance.

   The first controlled experiments with EM waves were done by Heinrich Rudolf Hertz (1857-1894) in 1888. The electric field associated with the waves was detected by a dipole antenna with a spark gap in the middle. The magnetic field was detected with apparatus similar to that at the right, which is at Vassar College. The changing magnetic field induced an EMF in the ring, causing sparks to jump between the two brass spheres at the top of the apparatus. Both experiments had to be done in a dark room to observe the minute sparks. 

   The Deutches Museum in Munich has Hertz' original apparatus; a reproduction, constructed by Samuel Devons, is at Barnard College.

   At the left is one of two identical Hertzian transmitters and receivers at the College of Wooster in Ohio. Originally a Leiden Jar was placed on top of the circular platform on the base. The circular loop acted as both the antenna and the inductor, and was placed in parallel with the Leiden jar capacitor to act as an LC resonant circuit. The only difference between the transmitter and the receiver was the induction coil that was connected to the transmitter.
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