Academic Reading — Test 128

Reading passage

For most of human history, the speed at which information travelled was limited by the speed at which a person, a horse or a ship could carry it. A message dispatched across an ocean might take weeks or even months to arrive, and a reply could not be expected until the same slow journey had been completed in reverse. The electric telegraph, developed during the first half of the nineteenth century, broke this ancient constraint by allowing words to be transmitted along wires almost instantaneously. The invention rested on the discovery that an electric current could be switched on and off in a controlled pattern, and that these patterns could be read at a distant point as meaningful signals. Several inventors contributed to the practical telegraph, but the system that came to dominate was associated with the American Samuel Morse. Working with colleagues in the 1830s and 1840s, Morse helped devise a code in which letters of the alphabet were represented by combinations of short and long pulses, commonly called dots and dashes. The code was simple enough to be learned by ordinary operators, and it required only a single wire to function. In 1844 a line was opened between Washington and Baltimore, and within a few years telegraph wires were spreading rapidly across both the United States and Europe. Governments, newspapers and businesses were quick to grasp the commercial value of receiving news and prices ahead of their rivals. Stringing wires across dry land was difficult but manageable; carrying a signal beneath the sea was a far greater challenge. A submarine cable had to be insulated so that the electric current would not leak away into the surrounding water, and it had to be strong enough to survive being laid across a rough and uneven sea floor. The key material proved to be gutta-percha, a natural latex obtained from certain trees in South-East Asia. Gutta-percha could be moulded around the copper conductor to form a waterproof coating, and unlike rubber it remained stable in cold water. A short cable across the English Channel, linking Britain and France, was successfully completed in 1851 and demonstrated that underwater telegraphy was genuinely practical. Encouraged by such successes, engineers turned to the formidable task of connecting Europe with North America across the Atlantic. The first attempt, made in 1858, did manage to carry messages for a short period, including a famous exchange of greetings between Queen Victoria and the American president. Within weeks, however, the cable failed, partly because excessive voltage had been applied in an effort to push signals through it. The setback was discouraging, and the outbreak of the American Civil War delayed further attempts. Critics argued that the whole enterprise was a waste of money, yet a determined group of investors and engineers refused to abandon the idea. The eventual triumph owed much to improvements in both manufacture and scientific understanding. The physicist William Thomson, later known as Lord Kelvin, studied how signals weakened and blurred as they passed along a long cable, and he designed sensitive instruments capable of detecting very faint currents. A far larger and better-insulated cable was produced, and the enormous steamship Great Eastern, the only vessel large enough to carry the entire length, was used to lay it. After a failure in 1865, a fully working transatlantic cable was completed in 1866, and the broken cable from the previous year was even recovered and repaired. From that point onward, messages could pass between the two continents in minutes rather than weeks. The consequences of this achievement were profound and lasting. Financial markets in distant cities could now respond to the same information at almost the same time, and diplomats could communicate with their governments far more quickly during a crisis. Over the following decades a dense web of submarine cables was laid across the world's oceans, linking the continents into a single network of communication. Much of this network was controlled by British companies, which gave Britain considerable influence over the flow of international news. Although the technology has since been transformed, first by radio and later by satellites and fibre-optic cables, the basic principle established in the nineteenth century endures. The vast majority of the world's intercontinental data still travels, as it did then, through cables lying on the bed of the sea.