FIG. 25. Hertzian Oscillator and Resonator.
Hertz employed an apparatus consisting of two metallic balls connected by metal rods to two metal sheets. The two balls were also connected to the secondary terminals of an induction coil. This apparatus comprised the oscillator and served to create the electro-magnetic waves.
In order to detect the waves, he employed a resonator consisting of a circle of wire having in it a minute spark gap capable of fine adjustment.
As soon as the coil is set in operation a spark snaps across the gap and sets up a temporary conducting path for the surgings that follow. Each spark sent by the coil across the gap consists of a dozen or so oscillations, each lasting less than a millionth of a second.
Then if the resonator is placed a few feet away from the oscillator and turned broadside on to the oscillator, it will be found that small sparks jump across the gap. Hertz employed various arrangements for reflecting and polarizing the waves and definitely proved that their nature is the same as that of light.
LESSON ELEVEN. ELECTRIC WAVES.
When a Leyden jar discharges under the conditions set forth in one of the previous lessons, portions of the energy of the current or discharge are thrown off from the conductor and do not return to it, but go traveling on in space.
If a current is sent through a circuit, as the current increases, the magnetic field also increases, the magnetic lines enlarging and spreading outward from the conductor like the ripples on a pond. If the current is decreased, the magnetic lines all return back and close up upon the conductor, the energy all being re-absorbed into the circuit.
If electrical oscillations of extreme rapidity such as those generated by a condenser discharge are substituted for a current slowly rising and falling, part of the energy radiates off into the ether as electromagnetic waves and only a part returns back.
The discharge of a Leyden jar or condenser only oscillates when the circuit contains a certain amount of capacity and inductance in proportion to the resistance of the circuit.