How it began
The compass was invented in China during the Han dynasty, between the 2nd century BCE and the 1st century CE, where it was called the south-governor (sinan). It was not at first used for navigation but for geomancy and fortune-telling. The Lunheng, composed by Wang Chong between 70 and 80 CE, records that a south-pointing spoon thrown upon the ground comes to rest pointing at the south. The passage has been widely considered a description of the earliest form of the magnetic compass.
How it works
Early compasses were made of lodestone, a naturally magnetic form of the mineral magnetite that aligns itself with the Earth's magnetic field. The lodestone was fashioned into the shape of a spoon or ladle and set on a flat, square bronze plate that represented the Earth, with a large circle at the center representing the Heavens. The handle of the spoon always pointed toward the south. A later device was a wooden fish containing a magnetized needle, floated in a bowl of water.
How it spread
The compass was in use for maritime navigation in China by 1111 to 1117. The typical Chinese navigational compass was a magnetic needle floating in a bowl of water. A dry suspension compass, in the form of a wooden turtle with a lodestone sealed inside by wax, was also used in the Song and Yuan dynasties, although it never became as common in China as the wet compass.
What changed first
The first uses were divination and the siting of buildings. The Wujing Zongyao, a Song dynasty military book of 1040 to 1044, describes an iron south-pointing fish floating in a bowl of water and recommends it for orientation when troops met gloomy weather or dark nights. In 1088 Shen Kuo's Dream Pool Essays gave the first incontestable description of a magnetized needle, made by rubbing a needle's tip with lodestone and hanging it from a single strand of silk.
What lasted
The compass is counted with papermaking, printing and gunpowder among China's Four Great Inventions. The National High Magnetic Field Laboratory states that the spoon and fish compasses paved the way for more precise instruments that allowed explorers to navigate the seas accurately. The cause of the needle's behavior was attributed to the supernatural in both Asia and Europe until about 1600, when William Gilbert published De Magnete.
