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 early peoples.  This was known as a clepsydra.  Fancy a tall glass tube with an opening at the bottom in which a sort of faucet was fixed.  At varying heights sentences were inscribed about the tube.  The tube, being filled with water, with, a float at the top, all was ready for signaling any of the messages inscribed on the tube to a station within sight and similarly equipped.  The other station could be located as far away as a light could be seen.  The station desiring to send a message to another exhibited its light.  When the receiving station showed its light in answer, the tap was opened at the bottom of the tube in each station.  When the float dropped until it was opposite the sentence 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 compare very favorably with the means employed by the ancients.  Smoke-rings and puffs for the daytime, and fire-arrows at night, were used by them for the sending of messages.  Smoke signals are obtained by building a fire of moist materials.  The Indian obtains his smoke-puffs by placing a blanket or robe over the fire, withdrawing it for an instant, and then replacing it quickly.  In this way puffs of smoke may be sent aloft as frequently as desired.