For explanation of the induction coil, see p. 122

"What is Electricity?" p. 46.

If a magnetized bar be heated to white heat and tapped with a hammer it loses its magnetism, because the distance between the molecules has increased, and the molecules can easily return to their original positions.

Named after their first discoverer, Dr. Hertz of Carlsruhe, "Hertzian waves."

For long-distance transmission powerful dynamos take the place of the induction coil and battery.

"Technics," vol. ii. p. 566.

In 1896 the late Li Hung Chang sent a cablegram from China to England (12,608 miles), and received a reply, in seven minutes.

From the Latin commuto, "I exchange."