Last week I was in London and, true to habit, I went to visit the London Science Museum. I spent a lot of time in the Information Gallery, specifically the exhibits dedicated to the development of the telegraph.

The telegraph, for the first time, made it possible to communicate almost instantly over long distances. In addition to speeding up the distribution of information it created a host of other problems. Things that we take for granted today like time zones can be traced directly to the telegraph.

The rest of this post is (an incomplete) timeline of the development of the telegraph. Don't take this to be a definitive history, it is simply a re-transcription of the notes I took during whilst exploring the exhibit.

1835

Morse makes his first telegraph.

1840

The printing telegraph appears.

In a printing telegraph, instead of having one button the operator would use a piano like keyboard to send a series of pulses along the cable. A machine on the receiving end would then decode the pulses and print out the text of the message directly without requiring an operator to translate it from Morse code.

1850

First cross channel telegraph wire laid.

A telegraph cable is laid from Britain to France. It was only about two centimetres in diameter and failed within an hour of completion. A second attempt in 1851 was successful and was used until 1875.

1852

The telegraph is used to propagate railway time in England.

Until railways brought towns closer together in an interconnected mesh each would have it's own time derived from the local solar time. Whilst not an issue for towns close to each other it was a problem when the task of expressing the timetables for trains in distant areas of the country.

The solution was railway time. The railway company expressed all the timetables in London time and kept "railway time" clocks in each station. However, precise mechanical clocks were still expensive and keeping the clocks synchronised throughout the country was a real challenge.

Enter the telegraph. Dedicated telegraph lines were used to connect stations to central clock. Every hour, on the hour, an electrical pulse would be sent on the wires. This allowed distant clocks to be regularly re-synchronised as they drifted away from the official time.

1857

The first transatlantic cable is laid.

No ship in the world at the time was large enough to carry the entire length of cable required to cross the Atlantic ocean so instead, two ships were converted, one in England and one in the United-States: the HMS Agamemnon and the USS Niagara. They set sail and met in the middle of the Atlantic to join their cables together. The first two attempts were failed when the cable broke and could not be retrieved.

A third attempt in 1858 was more successful however, when the two cables were about to be joined it was discovered that the armouring around the cables had been wound in opposite directions and, if directly connected they would unravel each other. A new splicing technique had to be improvised then and there to allow the two cables to be joined. The cable however failed after three weeks. The splice, fortunately, was not at fault.

In those early days it was impossible to amplify the signal which made the signal incredibly faint even when extremely voltages were used to send messages. To read such faint signals an ingenious invention was used: the TODO: (add wikipedia link) mirror galvanometer. This contraption uses a mirror suspended in the centre of a coil of wire. When a current passes through the coil a magnetic field is generated which deflects the mirror. When a light is shone on the mirror the deflection will cause a large change in the reflection of the light.

1858

Punched Tape Systems.

Very quickly humans were identified as a bottleneck. The telegraph lines could be better be put to use if only messages could be sent faster. This led to the development of mechanical machines to replace telegraph operators. In the punched tape systems an operator would encode a message onto a narrow strip of paper which would then be read by an automated machine. On the receiving end another machine would receive the telegraph and print it out on another strip of paper ready to be decoded by another operator.

1866

First successful transatlantic cable laid.

After the failures of 1857 and 1858 the interest for transatlantic cables waned. It was only in 1866 that a new cable was laid. This time a single ship, the SS Great Eastern was used. It was a passenger liner specially converted for the mission of cable laying and the only ship afloat capable of carrying the entire spool of cable.

1884

International Meridian Conference.

The telegraph has made the world smaller, distant areas can now communicate in close to real time and it becomes important to standardise time not only in countries but also world-wide. At the International Meridian Conference the world accepts the concept of 24 hour days based on the Greenwich meridian. This is the birth of GMT time.

1897

Time division multiplexing is used to improve the throughput of individual telegraph lines

Even with mechanisation there were still ways to increase the amount of messages that could be sent over a single telegraph line. One possibility was a time division multiplexing scheme in which several operators would share a single line. Their consoles were connected to a machine that connected them to the actual cable one by one at fixed intervals. In a scheme with 5 operators for example, each would receive 200 milliseconds every second in which to transmit their message. A machine on the other end would perform the opposite operation to decode the messages.