through a coil of insulated wire attached to a telephone receiver,
this sudden change in the magnetic field induces an electric current
in the surrounding coil and the operator hears a sound in the telephone
at his ear. The Morse code may thus be signalled from the distant
transmitter.

There are various systems of wireless telegraphy for the most part
called after the scientists who developed or perfected them. Probably
the foremost as well as the best known is that which bears the name
of Marconi. A popular fallacy makes Marconi the discoverer of the
wireless method. Marconi was the first to put the system on a commercial
footing or business basis and to lead the way for its coming to the
front as a mighty factor in modern progress. Of course, also, the honor
of several useful inventions and additions to wireless apparatus must
be given him. He started experimenting as far back as 1895 when but
a mere boy. In the beginning he employed the induction coil, Morse
telegraph key, batteries, and vertical wire for the transmission of
signals, and for their reception the usual filings coherer of nickel
with a very small percentage of silver, a telegraph relay, batteries
and a vertical wire. In the Marconi system of the present time there
are many forms of coherers, also the magnetic detector and other
variations of the original apparatus. Other systems more or less
prominent are the Lodge-Muirhead of England, Braun-Siemens of Germany
and those of DeForest and Fessenden of America. The electrolytic
detector with the paste between the tin blocks belongs to the system
of DeForest. Besides these the names of Popoff, Jackson, Armstrong,
Orling, Lepel, and Poulsen stand high in the wireless world.

A serious drawback to the operations of wireless lies in the fact that
the stations are liable to get mixed up and some one intercept the