A Little History

In 1820 Oersted performed an experiment where he showed a current flowing in a wire creates a magnetic field surrounding a wire. This led to the creation of the electromagnet. Some years later in the 1830s Morse took advantage of this to create an electric telegraph.

The Science behind it

First off, the electromagnet is the heart of the telegraph. A current carrying wire itself has a very weak magnetic field surrounding it. However, every time a loop of wire is wrapped around, say a bolt, the amount of magnetism keeps adding up. Eventually, there is enough magnetism to actually do something.

The telegraph is a simple loop circuit. When a telegraph key switch is pressed, the circuit is closed, and a current flows in the circuit and energizes the coiled loop of wire, the electromagnet. The electromagnet pulls a lever arm and makes a click. Releasing the key opens the circuit and the lever arm springs back up again.