Queen Elizabeth's doctor worked out that Earth itself is a magnet
Why does a compass point north? Before 1600, some blamed the pole star or a giant magnetic island at the top of the world. William Gilbert, physician to Elizabeth I, built a small spherical lodestone model of Earth, tested compasses around it, and concluded that the planet is one enormous magnet.
Gilbert, born in Colchester around 1544, earned his medical doctorate at Cambridge in 1569, practised in London, became president of the Royal College of Physicians in 1600 and served as the queen's physician from 1601 until her death. His book De Magnete, published in 1600, described experiments with that model globe, which he called a terrella. He was the first to argue that Earth's centre is iron, and he noted that cutting a magnet produces two smaller magnets, each with its own north and south poles.
He also gave us a word. Experimenting with rubbed amber, elektron in Greek, he used the Latin electricus to describe substances that attract like amber does, and Sir Thomas Browne turned it into the English word electricity in 1646. Gilbert built the first electroscope, a pivoted needle he named the versorium. Not everything held up: he insisted electricity and magnetism were separate forces, partly because he believed heat destroyed only the electrical effect. Hans Christian Ørsted and James Clerk Maxwell later showed they are aspects of one force. A 2011 Royal Society study also failed to repeat his method of magnetising hot iron by hammering it.
Gilbert argued that the daily turning of the sky came from Earth spinning, not from vast crystal spheres, some two decades before Galileo, and he suggested stars lie at varying distances. In the 1590s, without a telescope, he drew what may be the first map of the Moon's markings, though he guessed the bright patches were water. Francis Bacon mocked him for building a whole philosophy out of lodestones, yet later historians hailed De Magnete as a model of experimental science that preceded Bacon's own writing on method.
Gilbert died in London in 1603, probably of bubonic plague. A unit of magnetic potential, the gilbert, honoured him until the ampere-turn replaced it. His monument survives in a Colchester church that now houses a café.
Source: William Gilbert (physicist)
