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An English scientist and physician to Queen Elizabeth. Gilbert, also known as William of Colchester, performed important early studies of electricity and magnetism. He was the founder of the modern sciences of electricity and magnetism. In his famous book “De Magnete” (1600), he was the first to describe the earth’s magnetic field and to assume the relationship between electricity and magnetism. He introduced the term electricity.
Gilbert was among the first to divide substances into electrics (spar, glass, amber) and nonelectrics. William Gilbert was born in 1544 in Colchester, England, into a middle class family of some wealth. Until this century, Gilbert’s birth was universally placed in 1540. 1544 has now been established on good evidence. His father, Jerome Gilbert, was the recorder of Colchester. One source listed him as a merchant. Clearly his own forebears were merchants and made a fortune at it. None of the good sources says a word about Jerome Gilbert being a merchant, evidently prosperous.
William Gilbert entered St. John’s College, Cambridge, in 1558 and obtained an B.A. in 1561, an M.A. in 1564, and finally an M.D. in 1569. At Cambridge he became a Junior Fellow of St. Johns in 1561. He was the mathematics examiner in the college, 1565-6 and bursar, 1569-70. Upon receiving this last degree, in 1569, he became a Senior Fellow of the college, where he held several offices.
Gilbert set up a medical practice in London in the 1570s and in 1573 became a member of the Royal College of Physicians (the body that regulated the practice of medicine in London and vicinity). Gilbert, by the mid-1570s, was a prominent physician in London, consulted among others by the aristocracy. In 1600 he became president of the Royal College of Physicians and was appointed as a personal physician to Queen Elizabeth I. He received a pension of 100 pounds (which is hard to distinguish from a salary) from the Queen. He kept the position until Elizabeth died.
Apparently his duties as a personal physician to Queen Elizabeth I of England allowed him time to study several scientific questions. He was a scientist, or natural philosopher, to use the historical term, in his spare time. He is known to have inherited property from his father, and it is possible that he inherited Wingfield House, his residence in London, from his step-mother (a Wingfield), sometime before 1583. He never married. Gilbert spent 17 years experimenting with magnetism and, to a lesser extent, electricity. For his work on magnets, Gilbert became known as the “Father of Magnetism.” He discovered various methods for producing and strengthening magnets. For example, he found that when a steel rod was stroked by a natural magnet the rod itself became a magnet, and that an ion bar aligned in the magnetic field of the earth for along period of time gradually developed magnetic properties of its own. In addition, he observed that the magnetism of a piece of material was destroyed when the material was sufficiently heated.
He assembled the results of his experiments and all of the available knowledge on magnetism in the treatise “De Magnete, Magneticisque Corporibus, et de Magno Magnete Tellure” ("On the Magnet, Magnetic Bodies, and the Great Magnet of the Earth"), published in 1600. He introduced the term electric for the force between two objects charged by friction and showed that frictional electricity occurs in many common materials. He also noted one of the primary distinctions between magnetism and electricity: the force between magnetic objects tends to align the objects relative to each other and is affected only slightly by most intervening objects, while the force between electrified objects is primarily a force of attraction or repulsion between the objects and is grossly affected by intervening matter. Gilbert attributed the electrification of a body by friction to the removal of a fluid, or “humour,” which then left an “effluvium,” or atmosphere, around the body. The language is quaint, but, if the “humour” is renamed “charge” and the “effluvium” renamed “electric field,” Gilbert’s notions closely approach modern ideas.
London, 1600
The book starts with a resolve to strip away all myth from the subject and reason from observation: “In follies and fables do philosophers of the vulgar sort take delight; and with such like do they cram readers a-hungered for things obtruse, and every ignorant gaper for nonsense. But when the nature of the lodestone shall have been by our labours and experiments tested, then will the hidden and recondite but real causes of this great effect be brought forward, proven , demonstrated… and the foundations of a grand magnetic science being laid will appear anew, so that high intellect may no more be deluded by vain opinions". Gilbert was a believer in an animistic philosophy, and despite its modernity, the six books of De Magnete are cast in animistic and anthropomorphic terms.
Gilbert’s De Magnete book,
Gilbert dedicated the book to those who look for knowledge “not only in books but in things themselves.” Note that Gilbert, a prominent and probably wealthy physician, did not dedicate De Magnete to anyone. On the contrary, it is dedicated to Gilbert by Edward Wright, who wrote the dedicatory epistle.
From title page of the original Latin
Gilbert’s De Magnete quickly became the standard work throughout Europe on electrical and magnetic phenomena. Europeans were making long voyages across oceans, and the magnetic compass was one of the few instruments that could save them from being hopelessly (and usually fatally) lost. But little was known about the lodestone (magnetic iron ore) or magnetized iron. Gilbert tested many folk tales. Does garlic destroy the magnetic effect of the compass needle? More importantly, he made the first clear distinction between magnetic and the amber effect (static electricity, as we call it).
De Magnete is a comprehensive review of what was known about the nature of magnetism, and Gilbert added much knowledge through his own experiments. He likened the polarity of the magnet to the polarity of the Earth and built an entire magnetic philosophy on this analogy. In Gilbert’s animistic explanation, magnetism was the soul of the Earth and a perfectly spherical lodestone, when aligned with the Earth’s poles, would spin on its axis, just as the Earth spins on its axis in 24 hours. (In traditional cosmology the Earth was fixed and it was the sphere of the fixed stars, carrying the other heavens with it, that rotated in 24 hours.) Gilbert did not, however, express an opinion as to whether this rotating Earth was at the center of the universe or in orbit around the Sun.
One of Gilbert’s major discoveries was that the earth is a huge magnet, a connection that Peregrinus failed to make. He proved that a compass needle swings north because of the magnetism of the earth itself and not - as some believed - because of a star in the Big Dipper or a mysterious range of iron-capped mountains in the North. Using a spherical magnet and magnetic needle that was free to rotate in a vertical plane that included the magnetic poles of the sphere, he found that the needle dipped below the horizontal (the tangent plane to the sphere) at different angles, depending on its position on the sphere.
Gilbert realized that lines joining points of constant magnetic declination (the angle between the magnetic needle and the horizontal) were also lines of constant latitude on a sphere. Impressed with his discovery, he suggested an application to navigation. Although navigators used compasses at sea, they knew that variations in the earth’s magnetism often caused a compass to be unreliable. Gilbert thought circles indicating constant magnetic dip on the earth might be more reliable. However, navigators soon found that the dip along latitude lines varied considerably, and so the idea was abandoned. The growing interest in compass navigation may have influenced Gilbert somewhat because he wrote De Magnete at the time the English were preparing to meet the Spanish Armada. He specifically proposed the use of magnetic declination and dip to determine longitude and latitude. Thomas Blundevelle describes the two instruments of Gilbert’s invention intended for these purposes.
To understand better the Gilbert’s book impact, we should remember that Gilbert lived roughly the same period as Johannes Kepler. In 1600, when De Magnete was published, Giordano Bruno was burned at the stake in Rome because he believed in the Copernican theory. It was also the year in which Johannes Kepler set out to join Tycho Brahe in Prague. Since the Copernican cosmology needed a new physics to undergird it, Copernicans such as Johannes Kepler and Galileo were very interested in Gilbert’s magnetic researches. Galileo declared that he received a copy from a philosopher who feared that if he kept it on his bookshelf it would contaminate the other books with its new ideas. Many of the letters that Galileo exchanged with Fra’ Paolo Sarpi and with G. F. Sagredo reveal the great interest that the scientific community had for the book of William Gilbert at the beginning of the seventeenth century.
Galileo frequently underlined the striking combination of genuinely novel experimental results with credulousness in the writings of Gilbert. Because of his book, Gilbert has been called “the Galileo of magnetism". Galileo said De Magnete made Gilbert “great to a degree that is enviable.” In Gilbert’s work we find the beginnings of seventeenth century experimental observations into connected phenomena, and he provided a starting point for scientists of the next century. Galileo, the master experimentalist of his age, held Gilbert’s work in great esteem and the seventeenth century poet laureate John Dryden eulogized him with the lines:
“Gilbert shall live till the lodestones cease to draw
Or British fleets boundless oceans awe".
Gilbert extended his magnetic theories to include the cosmos. His theory that the earth exerted a magnetic influence throughout the solar system was a precursor to the modern conception of gravity as an attracting force between masses. He explained the diurnal rotation of the earth, postulated that the fixed stars were not all equidistant from the earth, and envisioned seas on the moon. He described the attraction of the moon to the earth and the tides as being magnetic in origin. Kepler tried to use magnetism to explain the force that swept the planets about the sun but he required so many ad hoc postulates that others found this theory unacceptable.
Gilbert made other interesting speculations, many of which would be confirmed decades later. For example, he considered comets to be wandering bodies without magnetic polarity that could be either within or outside the orbit of the moon. And he imagined a collection of stars in the Milky Way so numerous and so distant as to appear as a mist or cloud - years before the telescope would be invented and the Copernican system confirmed. He had also reached a correct view of the atmosphere as extending only a few miles from the surface of the earth, with nothing but empty space beyond. Although Gilbert discussed the motion of the earth according to Copernicus’s model, he neither confirmed nor denied the theory, perhaps fearing the same fiery fate as Giordano Bruno.
William Gilbert set out to debunk magical notions of magnetism, yet in building an intellectual bridge between natural philosophy and emerging sciences, he did not completely abandon reference to the occult. For example, he believed that an invisible “orb of virtue” surrounds a magnet and extends in all directions around it. Other magnets and pieces of iron react to this orb of virtue and move or rotate in response. Magnets within the orb are attracted whereas those outside are unaffected. The source of the orb remained a mystery. Although his language was that of the natural philosophy of the time, some of his ideas were ahead of his time. His orbs of virtue were a fledgling notion of the idea of fields that would revolutionize physics more than two centuries later.
“Terrella” - magnetic model of the Earth suggested by Gilbert
Sketch of Terrela
from William Gilbert’s ‘De Magnete’, 1600
‘Terrella’ is Latin for ‘little Earth’, the name given by Dr William Gilbert to a magnetized sphere with which he demonstrated to Queen Elizabeth I his theory of the Earth’s magnetism.
Scheme of compass movement around Terrele
from Practical Wireless, May 1997
By moving a small compass around the terrella and showing that it always pointed north-south, Gilbert argued that the same thing, on a vastly larger scale, was happening on Earth, and was the only reason why a compass pointed north-south.
Galileo’s efforts to make a truly powerful armed lodestone for his patrons probably date from his reading of Gilbert’s book. Later scientists such as Birkeland used the name “terrella” for magnetized spheres used inside vacuum chambers, together with electron beams, to study the motion of fast charged particles near the Earth. A sophisticated terrella experiment in a vacuum chamber is currently operated at the University of California at Riverside.
Although he is chiefly noted for his work in magnetism, Gilbert made many important contributions to the science of electricity, ranging from the invention of the electroscope to the study of conductors and insulators. To him we owe the term “electricity.”
When Queen Elizabeth I died in 1603, her only personal legacy was a grant to Gilbert to pursue his hobby, physics. After the death of Elizabeth he became King James I’s physician, but a few months later he was a victim of the plague. To the College of Physicians he left his books, globes, instruments and minerals, but they were destroyed in the great fire of London.
William Gilbert died on 30 November 1603 and was buried in Holy Trinity, an Anglican church, in Colchester where a monument was erected to his memory. The inscription on Gilbert’s tomb is modest. It reads: “He composed a book, concerning the magnet, celebrated among foreigners and among those engaged in nautical affairs.”
(There is also information that he was buried in Saint John’s College, Cambridge, England. The plate at left was pictured there).
Several of Gilbert’s unpublished and unfinished works were published in 1651 by his younger half brother under the title “De Mundo Nostro Sublunari Philosophia Nova” ("New Philosophy about our Sublunary World"). This work had little impact.
William Gilbert is remembered and his portrait even appeared in some art many years after his death: The Apotheosis of Power. Painted by Hugo Ballin, 1930. The figures on the right are Benjamin Franklin and Dr. William Gilbert.
The gilbert (Gi) is the CGS unit of magnetomotive force, equal to 10/4p = 0.795 775 ampere-turns, is named for him.
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