s they are purposely tuned. Atlantic liners now publish
daily small newspapers containing the latest news, flashed through space
from land stations. In the United States the De Forest and Fessenden
systems are being rapidly extended to embrace the most out-of-the-way
districts. Every navy of importance has adopted wireless telegraphy,
which, as was proved during the Russo-Japanese War, can be of the
greatest help in directing operations.

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

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

[15] "Technics," vol. ii. p. 566.

Chapter VIII.

THE TELEPHONE.

The Bell telephone--The Edison transmitter--The granular carbon
transmitter--General arrangement of a telephone
circuit--Double-line circuits--Telephone exchanges--Submarine
telephony.

For the purposes of everyday life the telephone is even more useful than
the telegraph. Telephones now connect one room of a building with
another, house with house, town with town, country with country. An
infinitely greater number of words pass over the telephonic circuits of
the world in a year than are transmitted by telegraph operators. The
telephone has become an important adjunct to the transaction of business
of all sorts. Its wires penetrate everywhere. Without moving from his
desk, the London citizen may hold easy converse with a Parisian, a New
Yorker with a dweller in Chicago.

Wonderful as the transmission of signals over great distances is, the
transmission of human speech so clearly that individual voices may be
distinguished hundreds of miles away is even more so. Yet the instrument
which works the miracle is essentially simple in its principles.

THE BELL TELEPHONE.

[Illustration: FIG. 62.--Section of a Bell telephone.]

The first telephone that came into general use was that of Bell, shown
in Fig. 62. In a central hole of an ebonite casing is fixed a permanent
magnet, M. The casing expands at one end to accommodate a coil of
insulated wire wound about one extremity of a magnet. The coil ends are
attached to wires passing through small channels to terminals at the
rear. A circular diaphragm, D, of very thin iron plate, clamped between
the concave mouthpiece and the casing, almost touches the end of the
magnet.

We will suppose that two Bell telephones, A and B, are connected up by
wires,