William Gilbert | Biography

William Gilbert was born in Colchester, Essex, England, on May 24, 1544. Although he was trained as a doctor and appointed court physician for a short time to both Queen Elizabeth I and King James I, Gilbert made his mark in the study of magnetism. His book De Magnete ("Concerning Magnetism"), established him as a physicist.

Petrus Peregrinus laid the groundwork of the understanding of magnetism some 250 years earlier. Gilbert built upon that framework. Like Peregrinus, Gilbert believed in experimentation to prove or disprove theory. Galileo credited Gilbert with being the founder of the experimental method, although history credits Galileo.

Gilbert discovered that a magnetic compass needle not only pointed north and south, it also "dipped" downward when influenced by a spherical magnet. He went on to discover that if the needle was freely suspended it "dipped," pointing toward the Earth. This "magnetic dip" led Gilbert to conclude that the Earth itself was a gigantic spherical magnet. Rather than pointing toward the north celestial pole, as Peregrinus had believed, the compass needle was pointing toward the north pole of the Earth's magnetic field.

Up until the time of Gilbert, lodestone was the only naturally occurring source of magnetism. Gilbert discovered he could create his own magnets. Rubbing an iron bar with a lodestone magnetized it. When the bar was heated, it lost its magnetic force and it could not be magnetized again until it had cooled. Gilbert's studies were so thorough, more than two hundred years would pass before additional knowledge of magnetism would be added. New advances weren't made until the time of Michael Faraday, founder of electrolysis, and William Sturgeon, who invented the electromagnet in 1823.

In addition to his work with magnetism, Gilbert pioneered the study of other attractive forces. It had been known since the time of the Greek philosopher Thales that when amber was rubbed it attracted other lightweight particles. Magnetism only affected iron, so some other force had to be responsible. What the force was remained a mystery to the Greeks.

Gilbert discovered that there were other objects, such as rockcrystal and gems, that when rubbed behaved the same as amber. In addition, the force of attraction was proportional to the size of the area being rubbed. The Greek word for amber was elektron, so Gilbert decided to label all these objects electrics, which ultimately led to the word electricity. The electric force became the second known force of attraction in nature. This paved the way for the discovery of "positive " and "negative" electric charges made by Charles Du Fay (1698-1739) in 1733.

Turning his attention from the Earth to the heavens, Gilbert speculated on the structure of the universe. He was the first prominent Englishman to be a strong supporter of the Sun-centered theory put forward by Nicholas Copernicus, and Gilbert wondered about the nature of the force that kept the planets in orbit around the Sun. He suggested that a form of magnetic attraction might be responsible. It was Isaac Newton who later determined it was gravity, not magnetism, that held the solar system together.

Gilbert's speculations in astronomy were far ahead of his time; he believed the stars were very large and distant. He also thought some of the stars might have inhabited planets orbiting them, an idea that is still popular today.

Gilbert died in London on November 30, 1603. Because of his pioneering work in the study of magnetic forces, magnetomotive force is defined in units of gilberts.