Karen Garvin
The Greeks and Chinese mentioned the phenomenon of magnetism as early as the sixth century BCE and fourth century BCE, respectively, when they noticed that certain types of rocks would attract small pieces of iron.[1] These rocks, known as magnetite, are a form of iron oxide and are very common.[2] Although the ancients made many attempts to explain how magnetism worked, its fundamental nature would remain a mystery until the nineteenth century.
Pliny the Elder (23–79 CE) described magnetite deposits in Spain and also noted that Ethiopia was a good source for magnets.[3] Large numbers of magnets were imported from India; however, few practical uses for magnets existed at the time. While some medical uses were mentioned in one of the Hippocratic treatises, and the stone was reported to have magical power, the main use of magnets seems to have been for their entertainment value.[4]
Magnets were commonly known as lodestones because of their ability to point in a specific direction. The word “lodestone” was coined around 1515, and is a combination of the Old English words “lād” (meaning direction or course) and “stān” (stone).[5] During the first century CE, the Chinese used a compass that incorporated a lodestone as a feng shui (Chinese geomancy) divining instrument to determine the best orientation for building sites. This device consisted of a bronze or wooden plate on top of which sat a spoon-shaped lodestone that could move freely to indicate direction (fig. 1).[6] The compass, or zhi nan zhen, was orientated with south as the primary direction.[7]
Figure 1. Han Dynasty compass with a south-indicating pointer. Creative Commons attribution-share alike 3.0 unported license, https://commons.wikimedia.org/wiki/File:Model_Si_Nan_of_Han_Dynasty.jpg.
Sometime around the twelfth century the Chinese developed a type of compass that used a magnetized needle floating in water.[8] Eventually the water was dispensed with, and a magnetized needle was pinned to a board that had an intricate design marked for feng shui purposes.[9] While this type of compass would later prove to be immensely useful to the Europeans for seafaring navigation, the Chinese continued to use a magnetized needle floating in water for navigation purposes until at least the sixteenth century.[10] When the compass arrived in Europe is uncertain; one theory suggests that the Venetian explorer Marco Polo (1254–1324) took it from China to Europe, while another theory suggests that Arab traders may have introduced it. Alternatively, the compass might have been independently developed in Europe.[11]
Theories of magnetism
Magnets were attributed with a wide range of magical and curative properties. No one had attempted to actually prove these claims until physician and philosopher William Gilbert (1544–1603) of England began to conduct formal experiments with magnets and electricity. In 1600, Gilbert published On the Magnet and Magnetic Bodies, and on That Great Magnet the Earth,