Fig. 295. ELECTRICAL RESONANCE EXCITER.
The method used for the production of rapid oscillations is the
following. To the terminals of an induction coil two metal spheres AA1
are connected as shown. This apparatus is termed the exciter; in its
discharge a series of isochronous discharges takes place, alternating in
direction. The period of duration T of a single one is given by the
formula T= 2* PI * squareRoot( LC ), in which C is the capacity and L
is the self-induction. The spheres may be 30 centimeters (11.8 inches)
in diameter, connected each to conductors 0.5 centimeter (.2 inch) in
diameter and 40 centimeters (15.7 inches) long each. For the length of
an undulation the formula gives for this apparatus 4.8 meters (15.75
feet) as the length of a wave, assuming for them the velocity of
propagation equal to that of light. The exciter may have 10,000 times
the rate of oscillation possessed by the plain induction coil.
When this apparatus is worked it produces induced waves in every
neighboring conductor. The resonance effects appear in the size of the
spark induced. Thus a wire bent into a circle with its ends nearly
touching will give a spark, but if made of proper electrostatic
capacity, corresponding with the particular waves employed, the spark
will be very much larger. The ring, with its spark gap is termed a
resonator. It is used as an explorer to trace the waves.
Waves thus produced are transmitted by stone walls and nonconductors in
general. A plate of zinc reflects part and transmits part. The reflected
waves can be traced by the resonator, their angle of reflection being
equal to their angle of incidence. They can be received by one parabolic
reflector, reflected to another and brought to a focus. They can be
reflected so as to produce interference or loops and nodes, and the
loops and nodes can be traced by the resonator. By a prism of asphalt
they are refracted exactly like light.
From all this it is concluded that an additional proof is furnished of
the identity of light and electro-magnetic waves, and a very strong
experimental proof of Maxwell's theory of light is furnished.
Synonym--Hertz's Experiments.