South Pointing Fish
The earliest reference to a specific magnetic direction finder device is recorded in a Song Dynasty book dated to 1040-44. There is a description of an iron “south-pointing fish” floating in a bowl of water, aligning itself to the south. The device is recommended as a means of orientation “in the obscurity of the night.” The Wujing Zongyao (武经总要, “Collection of the Most Important Military Techniques”) stated: “When troops encountered gloomy weather or dark nights, and the directions of space could not be distinguished…they made use of the [mechanical] south-pointing carriage, or the south-pointing fish.”[10] This was achieved by heating of metal (especially if steel), known today as thermo-remanence, and would have been capable of producing a weak state of magnetization.[10] While the Chinese achieved magnetic remanence and induction by this time, a similar discovery was not made in Europe until about 1600, when William Gilbert published his De Magnete.[11]
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