Chinese Compass

Before the invention of the compass, people had to rely on landmarks, constellations, or other visual means to help steer them in the right direction, and on a cloudy night or in a dense fog it was impossible.  In 221 BC, the magnetic compass was invented in China during the Qin dynasty.  Chinese fortune tellers set afloat in bowls of water tiny slivers of loadstone, (a mineral composed of an iron oxide which aligns itself in a north-south direction) the mineral now called magnetite, and discovered that the slivers quickly assumed a preferred direction.  The Chinese oriented it toward the south, and Indian Ocean accounts describe a magnetized iron fish floated in a bowl, whose head would point south to show direction at sea.  It is unfortunate that in 200 BC or around that date, the emperor destroyed all books and killed the scholars, so that earlier tales wouldn’t detract from his own greatness.

A lodestone is a powerful natural magnet also known as magnetite, which is a crystallized iron mineral with a black metallic luster.  There are different theories on how lodestone becomes magnetized.  One idea is that the strong magnetic fields surrounding lightning bolts change magnetite since lodestones are mostly found at the surface of our planet and are not buried deep in the Earth.  The directional property of lodestones was probably first used in the sinan ceremony, a practice evolved directly from the tradition of using a gnomon and the positions of the sun and stars to determine the time and directions.  The Sinan is similar to the household object ladle.  When it is placed on the divination utensil ‘Earth Disc,” its handle points to the south.  The utensil for indicating directions must have been a ladle-type pointing device made of lodestone.  Some people believe that Sinan is the constellation of the Big Dipper.

A gnomon is simply a vertical stick, which is called a ‘shadow stick’.  The gnomon is merely a vertical pole erected on a horizontal plane and the position of the Sun can be registered by the shadow cast by the gnomon.  With a simple gnomon it is possible to perform a large number of measurements fundamental to astronomy.  First, it is easy to find the meridian of the locality by bisecting the angle between the two positions of the shadow in which the shadows are of equal length.  In doing so, the four cardinal points on the horizon are also determined.  Next, the moment of true noon when the Sun is at its highest point in the sky, can be established, for then the shadow of the gnomon passes the meridian.  The date for the shortest noon shadow of the gnomon will then determine the moment of summer solstice.  Winter solstice is correspondingly established as the day when the noon shadow has its greatest length.  The length of the year (that is the tropical year) is found as the interval between two succeeding solstitial dates.

The magnetic compass directed the voyages of Chinese sailors by the middle of the ninth century AD.  Its use derived from the south pointing lodestone and a traditional ceremony referred to as the sinan ceremony.  Sinan can be translated as “south controller” or “south verification.”  Whatever its construction may have been, apparently it kept people engaged in various trades from getting lost.  The Chinese developed a lodestone compass to indicate direction sometime in the fourth century BC.  These compasses were south pointing and were primarily used on land as divination tools and direct finders.  Written in the fourth century BC, in the Book of the Devil Valley Master, it is written that “lodestone makes iron come” (or it attracts it).  The spoons were made from lodestone, while the plates were of bronze.

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