of three blocks.

The first vital experiments that led up to the invention of the
wireless telegraph were made by Heinrich Hertz, of Germany, in 1888
when he showed that the spark of an induction coil set up electric
oscillations in an open circuit, and that the energy of these waves
was, in turn, sent out in the form of electric waves. He also showed
how they could be received at a distance by means of a ring detector,
which he called a _resonator_

In 1890, Edward Branly, of France, showed that metal filings in a tube
cohered when electric waves acted on them, and this device he termed a
_radio conductor_; this was improved upon by Sir Oliver Lodge, who
called it a coherer. In 1895, Alexander Popoff, of Russia, constructed
a receiving set for the study of atmospheric electricity, and this
arrangement was the earliest on record of the use of a detector
connected with an aerial and the earth.

Marconi was the first to connect an aerial to one side of a spark gap
and a ground to the other side of it. He used an induction coil to
energize the spark gap, and a telegraph key in the primary circuit to
break up the current into signals. Adding a Morse register, which
printed the dot and dash messages on a tape, to the Popoff receptor he
produced the first system for sending and receiving wireless telegraph
messages.

[Illustration: Collins' Wireless Telephone Exhibited at the Madison
Square Garden, October 1908.]

After Marconi had shown the world how to telegraph without connecting