during the progress of the siege. Those at home would be eager for
news of the great enterprise. Many contingencies might arise which
would make the need for aid urgent. Certainly Queen Clytemnestra
eagerly awaited word of the fall of the city. Yet the slow progress of
couriers must be depended upon.

One device the king hit upon which was such as any boy might devise
to meet the simplest need. "If I can go skating tonight," says Johnny
Jones to his chum, "I'll put a light in my window." Such is the simple
device which has been used to bear the simplest message for ages. So
King Agamemnon ordered beacon fires laid on the tops of Mount Ida,
Mount Athos, Mount Cithæron, and on intervening eminences. Beside them
he placed watchers who were always to have their faces toward Troy.
When Troy fell a near-by fire was kindled, and beacon after beacon
sprang into flame on the route toward Greece. Thus was the message
of the fall of Troy quickly borne to the waiting queen by this
preconceived arrangement. Yet neither King Agamemnon nor his sagest
counselors could devise an effective system for expediting their
messages.

Prearranged signals were used to convey news in even earlier times.
Fire, smoke, and flags were used by the Egyptians and the Assyrians
previous to the Trojan War. The towers along the Chinese Wall were
more than watch-towers; they were signal-towers. A flag or a light
exhibited from tower to tower would quickly convey a certain message
agreed upon in advance. Human thought required a system which could
convey more than one idea, and yet skill in conveying news grew
slowly.

Perhaps the earliest example of marine signaling of which we know