De Magnete

Locale London, England

Date 1600

Gilbert, physician to Queen Elizabeth I, published the first great work of English science, De magnete, in which he presented his investigations into magnetic bodies and electrical attraction, opening up the study of electricity and magnetism and setting an example of experimental methods in science.

Key Figures

• William Gilbert (1544-1603), English physician, scientist, and philosopher
• Edward Wright (1558-1615), Cambridge cartographer and Gilbert’ collaborator
• Elizabeth I (1533-1603), queen of England, r. 1558-1603
• Francis Bacon (1561-1626), English philosopher and statesman

Summary of Event

William Gilbert of Colchester in County Essex, northeast of London, was trained in medicine at Cambridge University, completing his master of arts degree in 1564 and his doctor of medicine degree in 1569. He became a prominent physician in London, eventually serving as president of the Royal College of Physicians and royal physician to Queen Elizabeth I by 1600.

His most significant contribution came from nearly two decades of research on magnetism and electricity, encouraged by Elizabeth, who provided him with an annual pension for his philosophical studies. His research culminated in the one work published during his lifetime, De magnete, magneticisque corporibus, et de magno magnete tellure (1600; A New Natural Philosophy of the Magnet, Magnetic Bodies, and the Great Terrestrial Magnet, 1893), better known as De magnete.

De magnete was the first great book of English science, emerging during the scientific revolution. The work marks the transition from Renaissance naturalism to experimental science and was the first comprehensive treatment of magnetism since the Epistola de magnete (1269; Epistle of Peter Peregrinus of Maricourt to Sygerus of Foncaucourt, Soldier, Concerning the Magnet, 1902) of Peter Peregrinus. Its strong emphasis on observation and experiment (about fifty experiments are described) probably grew out of Gilbert’s collaboration with practical navigators and cartographers, especially the Cambridge mathematician, Edward Wright, England’s leading cartographer and expert on the compass. Wright not only provided practical information but also wrote the introductory address and chapter 12 of book 4 on magnetic declination (variation from true north). He also contributed to book 5 on magnetic dip (vertical inclination of the magnetic needle) and its relation to latitude, as well as designing an instrument for measuring dip.

The first of the six books in De magnete discusses the history of magnetism, refuting legends about the lodestone (naturally occurring magnetic stones) and describing its properties. Characteristically, Gilbert denied the Aristotelian concept of pure elements, and, in particular, elemental earth, to establish and advance his principle that Earth is a giant lodestone. He argued that this principle explains the phenomena of terrestrial magnetism. In so doing, he rejected the accepted view that the compass is attracted to the poles of the celestial sphere about which the stars and planets revolve. He described ways to demonstrate the behavior of the lodestone, marking his own experiments and discoveries with asterisks of varying size to indicate their relative importance. In the last five books, Gilbert discussed five magnetic movements, which he called coition, direction, variation, dip, and revolution.

Before proceeding with magnetic motions, Gilbert describes in book 2, chapter 2, his experiments on the amber effect to distinguish between magnetism and electricity, thus opening up a new field of study and naming it after the Greek word electron (meaning “amber”). He showed that some thirty different materials, including glass, hard sealing wax, and several semiprecious gems, have an attractive effect when rubbed. He called these materials “electrics” and distinguished them from “nonelectrics,” which do not exhibit an amber effect. He also described the working of the first electroscope, or versorium, by pivoting a metal needle on a post so that it would be deflected when a rubbed electric was brought near. He used an animate or formal cause to describe magnetism in which magnetic materials shared in the basic magnetic form or “soul” of Earth. By contrast, electric attraction is explained as a material cause in which electrics, when rubbed, emit “effluvia,” a kind of vapor that attaches to matter and pulls it inward.

In his study of magnetic phenomena, Gilbert assumed that every magnet is surrounded by an invisible “orb of virtue” (orbis virtutis) that affects any other magnetic material placed within its orb of virtue. He produced lathe-turned spherical lodestones, which he called terrellae (little earths), as laboratory models for the study of terrestrial magnetism. He preferred the word “coition” for magnetic attraction to emphasize that it was a mutual action between two magnetic bodies, each coming within the orb of virtue of the other. The direction or orientation of a magnetic compass is described in book 3 as the alignment of a compass needle with the earth’s magnetic orb of virtue rather than the celestial poles. To support this idea, he gave numerous demonstrations with a terrella, using small compass needles (versoria) to identify its poles as analogous with the earth’s north and south poles.

In book 4, Gilbert turned to variations in the orientation of the compass, the well-known declination of the magnetic needle from true north. He demonstrated a similar declination with a terrella by making a gouge on its surface analogous to the Atlantic Ocean and showing how such deviations from a smooth sphere affected the compass direction. He also discussed the possibility of using declination to determine longitude at sea. In book 5, he discussed the magnetic dip (inclination from the horizontal). Again using a terrella, he showed that there is no dip at the equator but there is increasing dip as the magnetic needle moves toward either pole. This led to the suggestion of using dip to measure latitude when the skies are clouded.

The last book of De magnete, book 6, discusses magnetic rotation, based on a suggestion in Peregrinus’s letter on magnetism that a spherical lodestone perfectly aligned with the celestial poles would rotate once every 24 hours. Gilbert floated a terrella on a cork raft and observed the terrella’s tendency to rotate into magnetic alignment. He suggests that magnetic rotation causes a daily rotation of the earth on its axis. Although he neither accepts nor rejects the heliocentric theory of the earth’s annual revolution around the sun, he does support Copernican ideas by denying the solid celestial spheres and their daily revolution, suggesting that the fixed stars are spread through space. He also suggests that the tides result from magnetism of the earth and moon. These extensions of magnetic philosophy were not as strongly supported by experiment and were the source of later criticisms of Gilbert’s work.

Significance

De magnete not only initiated the study of magnetism and electricity but also rejected natural philosophy and its support of new views of the world, including a mechanical explanation for the daily rotation of the earth. Its strong emphasis on experimental methods preempted ideas later developed by Francis Bacon. Ironically, the book was criticized by Bacon for its attempt to develop an entire philosophy based on magnetism and for the concept of a moving earth. The book was especially valuable for providing a modern understanding of terrestrial magnetism and the basis and terminology for later studies of electricity.

Most of Gilbert’s contemporaries, both in England and on the Continent, praised De magnete both for its content and for its new experimental methods. A second edition was published in 1628 and a third in 1633; it was widely distributed and it strongly influenced the emerging scientific revolution. Galileo Galilei (1564-1642) was greatly impressed and turned his attention to magnetic studies. Johannes Kepler (1571-1630) tried to incorporate Gilbert’s magnetic theory into an explanation of planetary motions in the Copernican system. Although the theory of the magnetic movement of the planets was later rejected, it provided a good explanation until the concept of gravitation could be further developed.

Bibliography

Gilbert, William. De magnete. New York: Dover, 1958. This reprint of P. Fleury Mottelay’s 1893 translation of De magnete includes a brief biographical memoir by the translator (containing some inaccuracies).

Margolis, Howard. It Started with Copernicus. New York: McGraw-Hill, 2002. This book discusses the work of Gilbert along with that of Simon Stevin, Kepler, and Galileo, in the context of the development of Copernican heliocentric theory.

Pumfrey, Stephen. “William Gilbert.” In Cambridge Scientific Minds, edited by Peter Harman and Simon Mitton. New York: Cambridge University Press, 2002. The first chapter in a book about Cambridge scientists that provides a good discussion of the context and contributions of Gilbert’s work.

Roller, Duane H. D. The “De Magnete” of William Gilbert. Amsterdam: Menno Hertzberger, 1959. This is probably the best single source on William Gilbert and his work.

Rossi, Paolo. The Birth of Modern Science. Malden, Mass.: Blackwell, 2001. Chapter 9, “Magnetic Philosophy,” begins with a discussion of Gilbert’s work and explores the development of Gilbert’s ideas by other scientists in the seventeenth century.

Verschuur, Gerrit L. Hidden Attraction: The History and Mystery of Magnetism. New York: Oxford University Press, 1993. Chapter 3, “On the Magnetical Philosophy,” is devoted to the work of William Gilbert.