in other words, it transforms, or changes the character of, electrical energy.
An induction coil is shown in Fig. 7, at the left. This is also known as a Ruhmkorff coil in honor of its inventor. By its use electrical energy at pressures which might scarcely be felt even when placed across the tongue may be transformed into pressures so great as to render a person unconscious, or to even cause death.
Another form of induction coil is called a transformer. The Ruhmkorff coil is operated by means of an interrupted unidirectional current, while the transformer is operated by an alternating current, i.e., a current which flows rapidly and alternately in opposite directions. Both of these devices are operated by, and consequently deliver, currents of very low frequency, as compared with the frequency required to generate the wireless waves.
8. Leyden-Jar Battery
A frequency of at least 100,000 vibrations per second is required to form the wireless waves, and since it is impossible to practically obtain this frequency by mechanical means, the Leyden jar is employed for this purpose. This device consists of two pieces of tin-foil separated and insulated from each other by glass, or other suitable material.
A group of these jars, when connected together, con-