30/09/2013 Physics Psychology
DOI: 10.1002/9781118606711.CH1 SemanticScholar ID: 142551247 MAG: 1561050042

What is Reading Comprehension

Publication Summary

In 1800 the British Empire started a titanic task: the costruction of a network of submarine cables to provide a rapid system of communication with the colonies and with other sovereign states. The success of the telegraph on the mainland had proved that messages could be transmitted through the use of an electrical circuit, but using the same system at sea presented greater difficulties. A technological problem was the choice of the right insulation for the cables. Indian rubber, then in use, corroded in water; the solution came from the discovery of a rubber in Malaysia, called gutta-percha, a natural thermoplastic that could be deformed with heat and hardens in cold seawater. The first cable linked Britain and France in 1851, but the real challenge was to place a transatlantic cable along the 3,700 kilometres between Ireland and Newfoundland (Canada) at a depth of 5–6,000 m. The first cables broke, and others transmitted a delayed, distorted and attenuated signal, but at the time there was no physical-mathematical theory for the propagation of electrical signals in long metal cables that could explain why. It was developed by William Thomson, the future Lord Kelvin (1824-1907). He discovered that the deterioration of the signal was caused by the resistance and capacitance of the cable: each of these variables is proportional to the length of the cable and the overall effect is proportional to the square of the length of the cable, a disheartening result. There was disagreement about what was the best constructive solution: some proposed a cable with a small diameter and an increase in the electrical voltage, while Thomson wanted to increase the diameter of the cable, lower the tension and improve the reception tools. For example, he proposed the use of a galvanometer mirror, which measures the current of the signal by amplifying the needle’s deviation through the use of a mirror. In 1857, the former solution was chosen; the voltage was increased to 2,000 V but it burnt the gutta-percha. Thomson’s solution then prevailed. In 1866 an efficient system was obtained: 8 words per minute. Thomson was awarded the title of Baronet for his merits.

CAER Authors

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Dr. Paula Clarke

University of Leeds - Associate Professor in Psychological Approaches to Childhood and Inclusive Education

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