Brief description

The telegraph is a communication system that transmits electric signals over wires from location to location. It translates mechanical action (tapping a key) into electrical pulses that produce a sound or mark at the receiving end.

Use / Function

• Primary use: Long-distance instantaneous communication.
• Secondary uses: Coordination of transport (trains), military command, time synchronization.
• Scale: From local (room to room) to continental.

Operating principle

Electromagnetism:

1. The Circuit: A battery is connected to a loop of wire that stretches between two stations.
2. The Transmitter (Key): A switch that normally breaks the circuit. When pressed, it completes the circuit, allowing electricity to flow.
3. The Receiver (Sounder): An electromagnet (a coil of wire wrapped around a piece of iron). When electricity flows through the coil, it becomes magnetic and attracts a movable iron arm (armature).
4. The Signal: The armature hits a stop, making a “click” sound. When the key is released, a spring pulls the armature back, making a “clack”.
5. The Code: Patterns of short and long clicks (dots and dashes) represent letters and numbers (e.g., Morse Code).

How to create it

1. The Electromagnet (Receiver)

• Wrap insulated copper wire around a soft iron core (like a large iron nail or bolt).
• Leave two ends of the wire exposed to connect to the circuit.
• Mount it on a wooden base.

2. The Sounder

• Mount a strip of flexible metal (iron or steel) or a hinged metal arm above the electromagnet.
• The metal must be close enough to be pulled down when the magnet is on, but spring back up when it’s off.
• Add a “stop” (a screw or nail) for the metal to hit to make a sharp sound.

3. The Key (Transmitter)

• Create a simple springy switch using a strip of metal screwed to a wooden block.
• When pushed down, it should touch a contact point (another screw) to close the circuit.

4. Connection

• Connect the Battery, Key, and Electromagnet in a single series circuit.
• For long distances, run two wires between stations, or use one wire and the Earth (ground) as the return path.

Materials needed

• Insulated Copper Wire: For the coils and transmission lines.
• Soft Iron: For the electromagnet core (nails, bolts). Soft iron loses magnetism quickly when power is cut (essential for fast signaling).
• Ferrous Metal Strip: For the armature (can be from a tin can or scrap iron).
• Wood: For the base and structure.
• Power Source: A battery (Voltaic pile or Daniell cell).

Variants and improvements

• Earth Return: Using the ground instead of a second wire saves 50% of the copper.
• Relay: For very long distances, the signal gets weak. A relay is a sensitive telegraph receiver that acts as a switch for a fresh local battery circuit, repeating the signal with full power to the next station.
• Sounder vs. Writer: Early versions marked paper tape; later operators preferred listening to the clicks (“Sounder”).

Limits and risks

• Resistance: Thin wires over long distances have high resistance, weakening the current. You need thicker wires, higher voltage, or relays.
• Privacy: Anyone tapping into the wire can read the message.
• Skill: Requires learning a code (like Morse) to use effectively.
• Weather: Lightning strikes on the line can destroy equipment and kill operators. Lightning arresters (spark gaps) are essential.