A closed circuit such as this is a feeble radiator and a feeble absorber, so it is not adapted for action at a distance. In fact, I doubt whether it will visibly act at a range beyond the ¼λ at which true radiation of broken-off energy occurs. If the coatings of the jar are separated to a greater distance, so that the dielectric is more exposed, it radiates better; because in true radiation the electrostatic and the magnetic energies must be equal, whereas in a ring circuit the magnetic energy predominates. By separating the coats of the jar as far as possible we get a typical Hertz vibrator (Fig. 5), whose dielectric extends out into the room, and thus radiates very powerfully. [Illustration: 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. [Illustration: FIG. 6.--Circular Resonator. (The knobs ought to nearly touch each other.)] [Illustration: FIG. 6A.--Any circular Resonator can be used as a sender by bringing its knobs near the sparking knobs of a coil; but a simple arrangement is to take two semi-circles, as in above figure, and make them the coil terminals. The capacity of the cut ends can be varied, and the period thereby lengthened, by expanding them into plates.]