FIG. 3.—A static machine connected to a Leyden jar.
The inner and outer coatings are connected to the terminals of a static electric machine (an apparatus for generating electricity), and the machine set in rotation. After the jar has been charged, the electric machine is disconnected and one end of a coil of heavy wire connected to the outside coating, while the other end of the wire is made to approach the knob connected with the inner coating. Before the end of the wire reaches the knob a discharge occurs through the coil, producing a noisy brilliant spark between the wire and the knob. The discharge appears like a single spark, but in reality it is composed of a great many following each other in rapid succession. The jar discharges its energy, first by a tremendous rush of current in one direction, and then another discharge somewhat smaller than the first in the opposite direction. There is a series of these discharges in reverse directions, but each discharge is less and less, until the whole amount of energy is expended. The complete series of discharges takes place in an almost immeasurable fraction of time. It is from this phenomenon that the electrical term "high frequency oscillations," so often heard of in "wireless" parlance, is derived.
FIG. 4.—A Leyden jar discharging through a coil of wire produces a brilliant spark and high frequency oscillations are created.
FIG. 5.—Curved line representing an oscillatory discharge of a Leyden jar.
FIG. 6.—Navy type of Leyden jars. Coated with copper deposited upon the surface of the glass.
High frequency oscillations are the "pebbles" which, dropped into the vast pool of ether, everywhere, set up "ripples" called electromagnetic waves (identical with the electromagnetic waves of light, but longer and so beyond the limits of our spectrum and the vision of the eye). The manner in which this is accomplished may be explained by saying that the charge creates a state of strain in the surrounding ether, and then abruptly releases it. Ether possesses a high degree of elasticity, so that when the state of strain is thus suddenly released, it immediately returns to its former state. The sudden motion of the ether results in waves which spread out from their source in enlarging circles.