Fig. 5.— Standard Hertz Radiator.
Ordinary Size Hertz Vibrator.
In consequence of its radiation of energy, its vibrations are rapidly damped, and it only gives some three or four good strong swings ([Fig. 1]). Hence it follows that it has a wide range of excitation; i.e., it can excite sparks in conductors barely at all in tune with it.
The two conditions, conspicuous energy of radiation and persistent vibration electrically produced, are at present incompatible. Whenever these two conditions coexist, considerable power or activity will, of course, be necessary in the source of energy. At present they only coexist in the sun and other stars, in the electric arc, and in furnaces.
Two Circular Vibrators Sparking in sympathy.
The receiver Hertz used was chiefly a circular resonator ([Fig. 6]), not a good absorber but a persistent vibrator, well adapted for picking up disturbances of precise and measurable wave length. Its mode of vibration when excited by emitter in tune with it is depicted in [Fig. 2]. I find that the circular resonators can act as senders too; here is one exciting quite long sparks in a second one.
Electric Syntony.—That was his discovery, but he did not stop there. He at once proceeded to apply his discovery to the verification of what had already been predicted about the waves, and by laborious and difficult interference experiments he ascertained that the previously calculated length of the waves was thoroughly borne out by fact. These interference experiments in free space are his greatest achievement.
Fig. 6.—Circular Resonator.
(The knobs ought to nearly touch each other.)