. His father, the aged AEgeus, seeing the black flag, believed
it reported his son's death, and, flinging himself into the sea, was
drowned.

In time it occurred to the great monarchs as their domains extended
to establish relays of couriers to bear the messages which must be
carried. Such systems were established by the Greeks, the Romans, and
the Aztecs. Each courier would run the length of his own route and
would then shout or pass the message to the next runner, who would
speed it away in turn. Such was the method employed by our own
pony-express riders.

An ancient Persian king thought of having the messages shouted from
sentinel to sentinel, instead of being carried more slowly by relays
of couriers. So he established sentinels at regular intervals within
hearing of one another, and messages were shouted from one to the
other. Just fancy the number of sentinels required to establish a line
between distant cities, and the opportunities for misunderstanding and
mistake! The ancient Gauls also employed this method of communication.
Caesar records that the news of the massacre of the Romans at Orleans
was sent to Auvergne, a distance of nearly one hundred and fifty
miles, by the same evening.

Though signaling by flashes of light occurred to the ancients, we have
no knowledge that they devised a way of using the light-flashes for
any but the simplest prearranged messages. The mirrors of the Pharaohs
were probably used to flash light for signal purposes. We know that
the Persians applied them to signaling in time of war. It is reported
that flashes from the shields were used to convey news at the battle
of Marathon. These seem to be the forerunners of the heliograph. But
the heliograph using the dot-and-dash system of the Morse code can
be used to transmit any message whatever. The ancients had evolved
systems by which any word could be spelled, but they did not seem to
be able to apply them practically to their primitive heliographs.

An application of sound-signaling was worked out for Alexander
the Great, which was considered one of the scientific wonders of
antiquity. This was called a stentorophonic tube, and seems to have
been a sort of gigantic megaphone or speaking-trumpet. It is recorded
that it sent the voice for a dozen miles. A drawing of this strange
instrument is preserved in the Vatican.

Another queer signaling device, built and operated upon a novel
principle, was an even greater wonder among the