Telegraphy spans the Atlantic - briefly

Electrical Tester – 1 November 2017

Author: Keith Wilson, Electrical engineer

When we think about telecommunications, we tend to imagine that it’s a relatively new art and that only a few decades ago people still had to resort to carrier pigeons to send messages! That’s not quite true, because the history of long-distance electrical communication goes back more than a century and a half.

In fact, the first transatlantic communication using the electric telegraph officially took place on August 16, 1858, although engineers’ test messages are certain to have been transmitted before this. It’s hard to overestimate the impact of this breakthrough, which reduced the communication time between North America and Europe from ten days – the time it took to deliver a message by ship – to mere minutes.

The story of transatlantic communication by telegraph starts two decades earlier in the 1840s when several inventors proposed the construction of a telegraph cable across the Atlantic Ocean. Edward Thornton, Alonzo Jackman, Samuel Morse, Frederic Gisborne, Cyrus Field and Charles Tilston Bright are among the prominent figures involved in the project.

Although over-ground telegraphy was already in use across Europe and some short undersea cables were also in operation, communicating between Europe and America posed much more of a challenge. Not only would the cable be under the sea for almost its entire length, there were severe problems with signal retardation that were not fully understood at the time.

Signals on the cable were transmitted using Morse code, with dots represented by one polarity and dashes by the opposite polarity. Retardation was a consequence of the time it took to charge and discharge the capacitance of the cable each time the polarity reversed, and it seriously degraded the signals, greatly reducing the signalling speed that could be achieved. With our present day knowledge, it’s easy for us to understand that the longer the cable, the more serious retardation effects would be the, and this was by far the longest cable to have ever been laid.

And as if things weren’t complicated enough, there were also practical manufacturing issues to consider: who would be able to manufacture such a long cable and how could it be laid? Importantly, how do you even lay a cable in water as deep as the Atlantic? This was all uncharted territory in more ways than one but, in the end, a cable was designed by Cyrus West Field and Charles Tilston Bright. With funding raised from both British and American investors, it was manufactured jointly by two English firms – Glass, Elliot & Co and R. S. Newall & Co.

The cable consisted of seven copper wires, each weighing 26 kg/km (107 lbs/nautical mile) covered with three coats of gutta-percha insulation weighing 64 kg/km (261 lbs/nautical mile), and wound with tarred hemp, over which a sheath of 18 strands, each of seven iron wires, was laid in a close spiral. The finished cable weighed nearly 550 kg/km. It was relatively flexible and was believed to able to withstand a pull of several tons.

Late in the manufacturing process it was discovered that the respective sections had been made with strands twisted in opposite directions. While the two sections proved a simple matter to join, this mistake subsequently became magnified in the public mind.

Following a brief inaugural message, the first official telegram to pass between two continents was a letter of congratulation from Queen Victoria of the United Kingdom to the President of the United States James Buchanan. There was great jubilation at the success of the venture, but this quickly proved premature. Signal quality declined rapidly and the transmission of messages, which was already painfully slow – Queen Victoria’s 98-word message took 16 hours to transmit – slowed further to an almost unusable speed. 

In a desperate attempt to achieve faster signalling Wildman Whitehouse, the engineer responsible for the operation of the cable from the American end, insisted on using higher and higher voltages derived from an induction coil, despite the concerns of Lord Kelvin, who was advising on operations at the European end. The cable soon failed completely – just three weeks after it had carried the first transatlantic message.

It has been argued that the faulty manufacture storage and handling of the 1858 cable would have led to premature failure, even if it had not been subjected to high voltages. Be that as it may, the cable’s rapid failure undermined public and investor confidence and delayed efforts to restore a connection. A second cable project finally went ahead in 1865 with much improved materials, and following some setbacks, the connection was completed and put into service on July 28, 1866. This cable proved more durable.

It is easy to look back at this first attempt and note what seem to us to be obvious mistakes and almost schoolboy errors that led to the demise of the first cable. However, without the industrious and creative ideas of the individuals involved, the progress of intercontinental telecommunications would likely have stalled at the stage of hand-written letters, transmitted via boats and ships, for many years longer.

As a footnote, it’s worth mentioning that there are, of course, enormous differences between a telegraph cable of 1858 and the cables in use today for the transmission of power. These cables do, however, have one thing in common: if you subject them to excessive voltage stress, they will fail. That’s why it’s always a good idea to choose cable test equipment that’s designed to minimise stress – an option that, sadly, wasn’t available to the transatlantic telegraphy pioneers of the 19th Century.