The Physics
An encyclopedia of scientific essays

The Two-Way Telegraph

search icon

The telegraph was a mechanism that was created to establish a connection between two people over a long distance. The telegraph was an amazing invention at its time because there was no way of communicating long distances. Samuel Morse created the telegraph and the code that is used to communicate. The telegraph communicates through a series of clicks; short and long to represent letters of the alphabet.

The telegraph works through electromagnetic principles. To set up a two way telegraph two different sets are required that are hooked up to each other in series with two power supplies. Initially, when the power is turned on, the circuit is open, and so there is no flow of electricity. The key is a means of closing the circuit. Whoever is receiving a message must keep their throwout switch closed. When electricity flows through the circuit, the electromagnets on each telegraph sounder are activated and they attract an iron strip attached to a brass hammer. When the electromagnet shuts off, a spring attached to the hammer returns the hammer to its original position. However, if the electromagnet pulls the hammer too far, the spring loses its ability to restore itself. An adjustable stop screw is used to maintain an appropriate balance; it prevents the hammer from coming too close to the magnet.

The telegraph works by alternately activating and deactivating an electromagnet, which pulls down a diamagnetic metal bar attached to a hammer on a pivot. The electromagnets are activated when the circuit is completed by pressing down a key, and deactivates the instant the circuit is broken. When the electromagnet is turned off, a spring returns the hammer to its initial position. If the metal bar touches the electromagnet, however, its magnetic force may overpower the force of the spring and prevent the bar from restoring itself. In order to balance the two forces, the hammer has one set screw above and one below it that regulate its maximum extension.

Schematic diagram of telegraph circuit

The two boxes on both end represent the base of the key and sounder. The two boxes in the middle represent the power supplies. The top switch and sounder creates one circuit and the bottom switch and sounder creates a second circuit.

Michael Calamara, Erik Hageman, Jerard Kneifati-Hayek, Leo Tam -- 2005