The invention of telegraph occurred around the 1820's, when the theory of electricity and magnetism was still developing. The telegraph works by sending electric pulses from one terminal to another. The electric pulses are generated by tapping on the device shown below. The electric pulses are then replayed back on the other terminal by an electromagnet. The electromagnet will move and make a tapping sound every time an electric pulse is received. The rhythm in the tapping allows people to encode messages.
The telegraph enabled almost instantaneous communication across vast distances, which was previously impossible. This was the first electrical communication device. This would lead to other communication devices, such as the telephone, the radio and eventually the Internet.
