22. Asea without a Compass: Celestial Way-Finding
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22 Asea without a Compass Celestial Way-­Finding The navigator recalls his sea lore, Remembers the guiding star for Ifaluk; When one is down, another rises. He remembers those stars Deep within him, Stars by which he can steer And grows impatient to be on his way. —song from Ifaluk Atoll, Caroline Islands As has been observed in previous chapters, many scholars—ignoring the feats of the Polynesians and others—have alleged that mariners could not have found their way around the vast open oceans without charts and without the compass and other instruments of relatively modern navigation. Even as early as the seventeenth century, the poet Abraham Cowley could versify, Our course by stars we cannot know, Without the compass too below. In this chapter, we shall see that this is far from being the case. Personal Magnetism: The Navigator’s Compass In 1620, Sir Francis Bacon declared that three relatively recent but initially obscure inventions—printing, gunpowder, and the magnetic mariner’s needle— all from China—“have changed the whole face and state of things through­ out the world.”1 It is to the third of these that we now turn. Knowledge of the property of certain iron-­ rich minerals, especially magnetite (lodestone), of attracting other fragments of those minerals or metallic iron, can be documented in the Mediterranean region back to at least the time of the sixth-­ century BC Greek, Thales of Miletos. The historian of mathematics Amir D. Aczel forwarded evidence of a link between lodestone divination, sixteen directions, and seafaring there going back into antiquity.2 However, in the West the first known mention of a magnetic direction-­ indicating device—simply a magnetized needle inside a straw floated on water—dates from only AD 1187. “With a floating needle,” claimed the historian Richard W. Unger, “skippers 234 / Chapter 22 were still limited to following the coast and to staying in port in the winter to avoid storms and cloudy skies.”3 Indications are that the first European appearance of the modern naviga­ tional compass was in Amalfi, Italy, around AD 1300, involving a dry-­ pivot ro­ tat­ ing magnetized steel needle combined with a sixteen-­ point compass card put into a box. Textual evidence suggests wide use of lodestone compasses in the north somewhat earlier, by about the middle of the thirteenth century AD. The European advent of the device, along with suitable charts on which to plot courses (beginning, in Italy, about AD 1250–65), is of­ ten said to have been among the late medieval/early Renaissance developments creating conditions that made Columbus’s crossing feasible. Aczel, who authored a 2001 comprehensive book on the topic, attributed supreme his­ tori­ cal importance to the instrument: Within a few decades of 1280, the world saw a dramatic rise in trade, and with it, increased prosperity. . . . A single invention—the magnetic compass—­ made this possible. The compass was the first instrument that allowed navigators . . . to determine their direction quickly and accurately at any time of the day or night and under almost any conditions. This allowed goods to be transported efficiently and reliably across the seas and opened up the world to maritime exploration. The earth would never be seen the same way again. The compass was therefore the most important technological invention since the wheel.4 Such hyperbole aside, it is generally recognized that the magnetic navigator’s compass was a Chinese, not a European, invention. North-­ and-­ south-­ pointing needles are described in an AD-­ 1044 Chinese text, and the use of the needle at sea is solidly attested by 1090. But nautical use is thought probably to have begun not long after AD 850, and somewhat earlier dates have also been suggested ; lack of early documentation likely reflects known Chinese secretiveness concerning the device. Knowledge of the principle of ferromagnetism itself is far older in China and could conceivably have been early employed at sea. Lodestone “south-­ pointers” (primarily for geomancy) are mentioned in fourth-­and first-­ century BC texts, and a third-­ century BC book refers to the device as ancient. It was a magnetite spoon, probably representing the Big Dipper, and was laid atop a dial-­ like diviner ’s board; it would rotate around the point at which the bowl rested upon the board. By 120 BC, a twenty-­ four-­ direction board was used. Ultimately, perhaps about AD 450, people found that an iron needle could be magnetized by rubbing it with lodestone, and this allowed much more precise...


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