For example, the second book, Mark the Mountain Guide and the Compass Adventure, includes a working compass & brief illustrated explanations of the history, science & technique behind magnetic needles used for navigation.
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Fahie, pp. 307–319 These served for switching the electric current. The receiving instrument consisted of six galvanometers with magnetic needles, suspended from silk threads. The two stations of Schilling's telegraph were connected by eight wires; six were connected with the galvanometers, one served for the return current and one for a signal bell.
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Astatic galvanometer, Nobili pattern at the Museo Galileo, Florence. An astatic system comprises two equal and parallel magnetic needles, but with their polarities reversed. This arrangement protects the system from the influence of the terrestrial magnetic field, as the magnetisms of the two needles cancel each other out. Because of this phenomenon, astatic needles were often used in galvanometers.
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The use of a compass as a direction finder underground was pioneered in the Tuscan mining town Massa where floating magnetic needles were employed for tunnelling, and for defining the claims of the various mining companies, as early as the 13th century.Ludwig and Schmidtchen, p. 62–64 In the second half of the 15th century, the compass became standard equipment for Tyrolian miners. Shortly afterwards the first detailed treatise dealing with the underground use of compasses was published by a German miner Rülein von Calw (1463–1525).
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Mohn (2003), 1. Shen discovered the concept of true north in terms of magnetic declination towards the north pole, with experimentation of suspended magnetic needles and "the improved meridian determined by Shen's [astronomical] measurement of the distance between the pole star and true north".Sivin (1995), III, 22. This was the decisive step in human history to make compasses more useful for navigation, and may have been a concept unknown in Europe for another four hundred years (evidence of German sundials made circa 1450 show markings similar to Chinese geomancer compasses in regard to declination).
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Five-needle telegraph receiving the letter G. The Cooke and Wheatstone telegraph consisted of a number of magnetic needles which could be made to turn a short distance either clockwise or anti-clockwise by electromagnetic induction from an energising winding. The direction of movement was determined by the direction of the current in the telegraph wires. The board was marked with a diamond shaped grid with a letter at each grid intersection, and so arranged that when two needles were energised they would point to a specific letter. The number of wires required by the Cooke and Wheatstone system is equal to the number of needles used.
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The Louth-London Royal Mail travelling by train from Peterborough East, 1845Although the idea of transmitting messages via electrical signals dated back to the eighteenth century, it was not until the 1820s that advances in the study of electricity and magnetism made that a practical reality. In 1837, William Fothergill Cooke and Charles Wheatstone invented a telegraphic system that used electrical currents to deflect magnetic needles, thus transmitting coded messages. This design soon made its way all across Britain, appearing in every town and post office. By the mid-1800s, a telegraphic cable was laid across the English Channel, the Irish Sea, and the North Sea.
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During this cycle, Edward Sabine, Rudolf Wolf, and other scientists recognized that solar disturbances affected the Earth's magnetic environment, so that solar cycles are identical to the Earth's geomagnetic cycles. Wolf also introduced the Wolf number during this period. The phenomenon now known as geomagnetically induced current was seen for the first time during this cycle – it became apparent on the emerging electric telegraph network. Francis Ronalds, Honorary Director of the Kew Observatory and Sabine's colleague, received data from telegraph operators on the movements of their magnetic needles for comparison with his own photo-recordings of atmospheric electricity and geomagnetic intensity variations but had insufficient resources to study the causes of the unexpected currents in detail.
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Shen Kuo asserted that the needle will point south but with a deviation, stating "[the magnetic needles] are always displaced slightly east rather than pointing due south." Shen Kuo wrote that it was preferable to use the twenty-four-point rose instead of the old eight compass cardinal points — and the former was recorded in use for navigation shortly after Shen's death. The preference of use for the twenty-four-point-rose compass may have arisen from Shen's finding of a more accurate astronomical meridian, determined by his measurement between the pole star and true north; however, it could also have been inspired by geomantic beliefs and practices. The book of the author Zhu Yu, the Pingzhou Table Talks published in 1119 (written from 1111 to 1117), was the first record of use of a compass for seafaring navigation.
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The work is a 48-page pamphlet that appears to be a printed version of a lecture he had given some years previously while teaching at the Jesuit seminary in Heiligenstadt. It is a mixture of descriptions of Kircher’s own experiments and accounts drawn from classical authorities. He describes his own attempts to measure the force of a magnet by using a balance, relates how an eruption of Vesuvius caused magnetic needles to change direction, and wonders that a red-hot piece of iron is attracted by a magnet, although the magnet is not attracted by it. He also suggested that magnetism could serve as a basis for long-distance communication. He cited the works of Pliny and Plutarch and suggested conserving a magnet’s strength by wrapping it in dried woad leaves. He warned that leaving a magnet near a diamond or rubbing it with garlic would weaken it, but its strength could be regained by pouring boar’s blood over it.
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