Telegraph sounder
The electromagnetic telegraph sounder — the device that made long-distance communication possible. An electromagnet pulls an armature lever down with a click, and a spring pulls it back up with another. Short clicks are dits, long ones are dahs. Type a message to transmit, or tap manually with the spacebar to key your own Morse code.
dit = 1 unit dah = 3 units letter gap = 3 units word gap = 7 units
The telegraph revolution
Samuel Morse’s telegraph, demonstrated publicly in 1844 with the message “What hath God wrought,” fundamentally changed human communication. For the first time, messages could travel faster than any person or animal. The telegraph compressed the world, making news from distant cities available in minutes rather than days or weeks.
How the sounder works
The telegraph sounder is elegantly simple. When electric current flows through the coil of an electromagnet, it creates a magnetic field that pulls down a hinged metal armature (lever). The armature strikes a metal anvil with an audible click. When the current stops, a spring pulls the armature back up, producing a second click. Skilled operators learned to distinguish dits (short current) from dahs (long current) by the rhythm of the clicks, reading messages by ear at speeds up to 30 words per minute.
Morse code timing
International Morse Code uses precise timing ratios. A dit is one time unit. A dah is three units. The gap between elements within a letter is one unit. Between letters, three units. Between words, seven units. The word “PARIS” takes exactly 50 units, so the WPM rate equals the number of times PARIS can be sent per minute. At 15 WPM, one unit is 80 milliseconds.
The electrical circuit
A basic telegraph circuit consists of a battery, a telegraph key (switch), a length of wire (the “line”), and the sounder. When the operator presses the key, the circuit closes and current flows through the sounder’s electromagnet. The same circuit could span hundreds of miles, with relay stations amplifying the signal. The earth itself served as the return path, eliminating the need for a second wire.