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Looking for the electric telegraph

Early experiment with lightning

Stephen Gray discovers conductivity (1729) : suspended on silken threads

The core technology of the telegraph involves sending electrical charges down lengths of wire. The first step towards discovering how to do thiswas taken by the English scientist Stephen Gray.

In the early 18th century Gray demonstrated that static charges of electricity could be conducted by some materials (for example wet twine) for distances as great as 765 feet while others (such as silk thread), did not conduct electricity at all.

Eventually he was able to send charges through 88 metres of wire suspended on silken threads to operate an electroscope - an instrument used to detect static electricity. In other words, Gray sent an electrical signal from one place to another in a way that made something happen at the other end - the basic principle of the electric telegraph.

Scots Letter, 1753

The Scots Letter (1753) : but who was he ...?

The first ideas for an electric telegraph were outlined more than 80 years before the first working device was actually patented.

In 1753 an anonymous writer 'C.M.' wrote a letter to the Scots Magazine that suggested using an array of 26 wires - one for each letter of the alphabet - to send messages over long distances. Most people think this writer was a Renfrew inventor called Charles Morrison - but whoever he was, he sowed the seeds of an idea that many others would take up over the next half century.

In 1774 a French inventor, Georges Louis Lesage, actually set up a multiple wire telegraph at Geneva. He sent messages through it in more or less the same way as suggested in the Scots Letter more than 20 years before. When an electric charge was applied to a wire at one end, it operated a pith-ball electroscope at the other. Lesage's system used insulated wires, one for each letter. The trouble was his telegraph only extended between two rooms of his house. It would have been much easier and quicker to shout...

One of the more bizarre applications of the Scots Letter idea was dreamed up by the Catalan scientist Don Francisco Salva i Campillo. Also making use of a separate wire for each letter of the alphabet, he suggested perhaps doing without electroscopes and using people instead. Upon receiving an electrical shock, they would call out the name of the letter of the alphabet assigned to them!

In the end, though, Salva created a much simpler - and more humane - single wire system between Madrid and Aranjuez in 1798.

He was also the first to suggest insulated telegraph cables running either underground or beneath the sea. Before that, people had envisaged only overhead wires.

Illustration of Volta's pile

Volta's pile - the first battery (1800) : from frogs to electricity

In 1780 the Italian anatomist Luigi Galvani constructed a crude electric cell with two different metals and the natural fluids from a dissected frog. Benjamin Franklin in the USA and George Adams in England were also studying the possible medical benefits of electricity around this time. But the more immediately useful result of Galvani's experiment was the electric battery.

In 1800 Alessandro Volta modified Galvani's cell by substituting other metals and replacing the frog tissue with wet pasteboard, creating a stack of several cells; the result was an electrical battery capable of holding a significant charge of several 'volts' (named after Volta).

There was great hope of using the galvanic battery in medical cures, even of bringing the dead back to life - with some bizarre experiments on the bodies of recently hanged criminals. But what it really meant was that for the first time there was a source of electric current that could be stored - and turned on and off at will.

Portrait of Oersted

Oersted links electricity and magnetism (1820) : an accidental breakthrough

The Danish physicist Hans Christian Oersted, noticed something that was to have astounding long term consequences. Oersted accidentally placed a magnetic compass next to an electrical wire. He noticed that whenever current flowed through the circuit, the compass needle swung to point directly at right angles to the line of the wire. Thus Oersted accidentally discovered the direct link between electricity and magnetism. This meant that 'pulsing' an electric current through the circuit could be used to make things happen at the other end of the circuit - the basic principle of the electric telegraph. It was left to the Frenchman Andre Ampere to explain precisely why this happened.

 
Portrait of Ampere

Ampere investigates electrodynamics (1820) : advancing current thinking

Andre Marie Ampere was Professor of Analysis at the Ecole Polytechnique at Paris when he heard of Oersted's discoveries in September 1820.

Only a week later, Ampere demonstrated before the Academy of Sciences another remarkable fact, that parallel wires carrying currents magnetically attract or repel each other, depending on whether the currents are flowing in the same or in opposite directions. This laid the foundation for the science of electrodynamics - the mechanical forces between current-carrying conductors that form the foundations for the telegraph, telephone receivers, microphones and loudspeakers.

Ampere went on to quantify how electrical currents behave and how to measure them. That is why the unit of electrical current - the ampere (or 'amp') is named after him.

fun and games

Can you beat our games? Explode equipment to see what's inside, hear the changing sounds of telecommunications, see how telecommunications designs have changed over time or send an e-postacard.

what's on

The UK's first permanent gallery dedicated to the history of information and communication technologies opens in the new Information Age gallery at London’s Science Museum.

audio history

Take a trip down memory lane with extracts of the interviews which have been recorded as part of the Connected Earth oral history programme.

featured story

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