The Boy Spy by Joseph Kerby description:
The Only Practical History of War Telegraphers in the Field–a Full Account of the Mysteries of Signaling by Flags, Torches, and Rockets–Thrilling Scenes of Battles, Captures and Escapes
er-tips gently against the armature and noting its pulsations. I thus became by practice not only proficient, but expert in telegraphy. Telegraphers know, though the general public may not, that messages can be sent by touching together the ends of a cut telegraph wire, and can be received by holding the ends to the tongue. My tongue, however, has always been too sensitive to take that kind of "subtle fluid."
Telegraphers have many methods of secret communication with each other: rattling teaspoons or tapping knives and forks at the table, or the apparently aimless "Devil's tattoo" of the fingers on the table or armchair are common methods, and I have heard of one in a tight corner who winked out a message appealing for help. It might be well to avoid playing poker at a table where two telegraphers are chums, for it is possible that one might learn when to stay in a little longer for the raise and make a pot a little bigger.
When Colonel Thos. A. Scott became Assistant Secretary of War