Shen Kuo
Magnetic needle compass

Since the time of the engineer and inventor Ma Jun (c. 200–265), the Chinese had used the south-pointing chariot, which did not employ magnetism, as a compass. In 1044 the Collection of the Most Important Military Techniques (武經總要; Wujing Zongyao) recorded that fish-shaped objects cut from sheet iron, magnetized by thermoremanence (essentially, heating that produced weak magnetic force), and placed in a water-filled bowl enclosed by a box were used for directional pathfinding alongside the south-pointing chariot.

However, it was not until the time of Shen Kuo that the earliest magnetic compasses would be used for navigation. In his written work, Shen Kuo made the first known explicit reference to the magnetic compass-needle and the concept of true north. He wrote that steel needles were magnetized once they were rubbed with lodestone, and that they were put in floating position or in mountings; he described the suspended compass as the best form to be used, and noted that the magnetic needle of compasses pointed either south or north. Shen Kuo asserted that the needle will point south but with a deviation, stating " 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. However, Zhu Yu's book recounts events back to 1086, when Shen Kuo was writing the Dream Pool Essays; this meant that in Shen's time the compass might have already been in navigational use. In any case, Shen Kuo's writing on magnetic compasses has proved invaluable for understanding China's earliest use of the compass for seafaring navigation.
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