2nd exam - 9/26/11 William Gilbert and the magnetic Earth...

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9/26/11 William Gilbert and the magnetic Earth Stephen Pumfrey, Latitude and the Magnetic Earth 2002 His work De Magnete one of the most influential works at the start of the scientific revolution. Idea that magnets held the key to understanding all sorts of things in nature. Also big on experimental science. Contemporary to Francis Bacon but they didn’t get along even though they were closer to each other than many others. Magnets weren’t a new discovery in the 16th century, known for a long time. Sometimes they were called lodestones, seen as mysterious and magical; occult quality (in the sense of being hidden, a quality that isn’t visible or sensible to us directly but it has effects on other things) . They attracted each other and was a strange behavior for rocks. Many theories in ancient and medieval world were not satisfactory. Often they ascribed some sort of life or soul that made the magnet move itself and other things, though how that worked wasn’t always clear. Did not fit well with Aristotelianism; medieval scholars offered only vague theories based on neo-Platonic idea of sympathies . Ancient Greeks and western world new of attraction of magnets, but the magnetic needle to always point north was first discovered through the Chinese, then used by the Arabs and Europe learned of the magnetic compass through them. Italian sailors learned it by 1100s from Arabs and it was very useful. They treated the construction of the mariner’s compass as a form of natural magic , and it was surrounded by ritualized practices. Ascribed directive property of magnets to sympathetic influence of celestial poles (the north star). Elaborate rituals to get a magnetic effect, to get it to point to the north star. They didn’t think about the Earth effecting the magnet. Thought of as a celestial influence. As Europeans sailed into the Atlantic in 15th and 16th centuries, they encountered variation : compass needles did not point due north, but were off by an amount that varied from place to place. Efforts to use this to find longitude failed; variation proved to be too inconsistent. This was very important because you no longer could use it as a completely reliable way to north, had to have some sort of standard for variation dependent on your location. You start to see on maps at the time that the compass rose would be drawn differently/changed according to the area of the map. Evidently the further north you are, the more it points down and not just pointing horizontally. Governments put up huge rewards for ways of finding longitude at sea. William Gilbert 1544-1603: learned English physician and natural philosopher, not a sailor. Probably the first important English physician, became the royal physician to Queen Elizabeth I. Was a great student of magnetism which he related to a broader philosophy. This was a great era of english explorers and sailors. Becoming more common to describe your discoveries/information/publications as “new” which became a
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2nd exam - 9/26/11 William Gilbert and the magnetic Earth...

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