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Development of the telegraph

Wheatstone ABC telegraph, Post Office pattern - a Connected Earth artefact, now at Amberley Museum

Alphabetic telegraphs : dialling a letter

The main problem with early telegraphy was that the machines and codes were complicated and specialised - which meant they needed highly trained operators.

The telegraph companies soon began to search for simpler systems that almost anyone could operate.

One of the first solutions was developed by the British pioneer, Professor Charles Wheatstone.

His ABC Telegraph, patented in 1858, featured two rotary dials. The upper dial displayed incoming messages and the lower dial was for outgoing ones. To send a message, you spelt it out by pressing the lettered buttons in turn, all the while turning the handle to send the sequence of letters. Each letter was then displayed on the incoming message dial at the other end of the line.

Hughes Telegraph

Keyboard systems (1858) : 'sitting at my piano'

It was pretty obvious from the start of telegraphy that, to be really useful, telegrams should be printed directly at the receiving end - without the need to 'decode' messages.

By 1858 the British professor David Hughes had developed just such a system. His telegraph worked from a piano-type keyboard with 28 keys and a 'shift' that allowed upper or lowercase letters to be chosen.

The key operated a typewheel (which had the letters and numbers on it, somewhat like a golfball electric typewriter) that whirled round to find and print each new character. A good operator could send up to 30 words a minute. But that was the trouble - the Hughes telegraph also demanded skilled operators because it had to be operated rhythmically, in time with the rotation of the print wheel.

Baudot distributor and keyboard

Baudot develops a new code (1874) : faster than Morse

Jean-Maurice-Emile Baudot was a French engineer who, in 1874, took out a patent on a telegraph code that used five-unit combinations of 'on' or 'off' signals of equal duration.

This was less error-prone and provided substantial advantages over the Morse system using combinations of short dots and long dashes. In particular, it was ideally suited for use in machine telegraphs

By the mid-20th century, Baudot's system had supplanted Morse Code as the most commonly used telegraphic alphabet.

In 1894 Baudot also invented a 'distributor' system for simultaneous transmission of several messages on the same telegraphic circuit or channel (multiplexing).

The Baudot code was accepted by the French administration in 1875. It saw widespread service in France and other countries and the British Post Office adopted it for a simplex circuit between London and Paris in 1897.

Later, Baudot refined and expanded the system to become faster and easier to operate.

Telegraph boys at Training School, 1930s

Limitations : it will get there - eventually

The telegraph was a lot quicker than a messenger - but it was far from instant.

It took time to send the messages and more time to decode them and/or write them out at the other end. Besides, the telegraph only connected operators - not the people sending and receiving the messages.

So the telegraph had some similarities to email. You could send your message - but you could not guarantee when it would actually reach the person you wanted to contact.

Delaney's multiplex distributor - a Connected Earth artefact, now at Amberley Museum

Delaney multiplex (c1882) : the more the merrier

Multiplex systems were introduced to use the spare capacity available on the telegraph network, either by using different tones or frequencies for simultaneous messages or by sharing a line, as this system did.

Each operator had to prepare the code for a word before it could be sent and this left small gaps between each transmission. Delaney realised that if several operators used the same wire, one after the other, they could use the gaps left while the other prepared the next code. This was known as time division multiplex (TDM).

This multiplex system briskly rotated so that each operator was connected to the network for a short time before the connection passed on the next person.

As long as everyone kept in time, and was ready when it was their turn, multiplexing improved efficiency immensely.

High-speed Wheatstone printer (1880s) : more Morse per second

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High-speed Wheatstone printer (1880s)

There is a limit to how fast an operator can work with Morse code, both in sending and receiving. A skilled worker can manage around 32 words per minute. This high-speed model allowed messages to be sent at hundreds of words per minute, freeing up valuable connection time.

At the base is a large roll of ticker taper, which is fed up through the mechanism. This passes under a wheel (connected to an inkwell), which is triggered by the incoming electrical message to leave marks in Morse code. The message itself is sent by a similar machine running tape with holes punched out of it in code format.

A separate motor, controls the speed of the tape and this can be sped up or slowed down by sliding the accelerator lever on the top to make sure the message lines are evenly and legibly spaced.

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.

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