centuries the people of the world existed, devising nothing better
than the primitive methods outlined above.




II

SIGNALS PAST AND PRESENT

Marine and Military Signals--Code Flags--Wig-wag--Semaphore
Telegraphs--Heliographs--Ardois Signals--Submarine Signals.


In naval affairs some kind of an effective signal system is
imperative. Even in the ordinary evolutions of a fleet the commander
needs some better way of communicating with the ship captains than
despatching a messenger in a small boat. The necessity of quick and
sure signals in time of battle is obvious. Yet for many centuries
naval signals were of the crudest.

The first distinct advance over the primitive methods by which the
commander of one Roman galley communicated with another came with the
introduction of cannon as a naval arm. The use of signal-guns was soon
thought of, and war-ships used their guns for signal purposes as early
as the sixteenth century. Not long after came the square-rigged
ship, and it soon occurred to some one that signals could be made by
dropping a sail from the yard-arm a certain number of times.

Up to the middle of the seventeenth century the possibilities of