which it was desired to transmit, the sending station withdrew its
light and closed the tap. This was a signal for the receiving station
to stop the flow of water from its tube. As the tubes were just alike,
and the water had flowed out during the same period at equal speed,
the float at the receiving station then rested opposite the message to
be conveyed.

Many crude systems of using lights for signaling were employed. Lines
of watch-towers were arranged which served as signal-stations. The
ruins of the old Roman and Gallic towers may still be found In France.
Hannibal erected them in Africa and Spain. Colored tunics and spears
were also used for military signals in the daytime. For instance,
a red tunic displayed meant prepare for battle; while a red spear
conveyed the order to sack and devastate.

An ancient system of camp signals from columns is especially
interesting as showing a development away from the prearranged signals
of limited application. For these camp signals the alphabet was
divided into five or six parts, and a like number of columns erected
at each signal-station. Each column represented one group of letters.
Suppose that we should agree to get along without the Q and the Z
and reduce our own alphabet to twenty-four letters for use in such
a system. With six columns we would then have four letters for each
column. The first column would be used to signal A, B, C, and D. One
light or flag shown from column one would represent A, two flags
or lights B, and so on. Thus any word could be spelled out and any
message sent. Without doubt the system was slow and cumbersome, but it
was a step in the right direction.

The American Indians developed methods of transmitting news which