William Gilbert’s On the Loadstone and Magnetic Bodies, and on the Great Magnet the Earth is a Latin treatise of experimental natural philosophy, published in London in 1600 and presented here in P. Fleury Mottelay’s English translation. Gilbert, a Colchester-born physician and president of the Royal College of Physicians, spent some eighteen years on the work, and its six books move from the properties of individual magnets to the claim that the earth itself is one. It is a founding document of experimental science: its arguments rest on instruments, repeated trials, and small iron needles rather than on ancient authority.
“One loadstone far surpasses another in energy, for one will snatch up almost its own weight of iron, while another is hardly able to move the smallest particle.”
The Core Argument
Gilbert’s central claim is that the earth is a great loadstone. Magnetism is not an occult curiosity of a rare stone but the fundamental form of the terrestrial globe, and the same force that makes a compass needle point north holds the world’s mass together. From this it follows that the loadstone and iron share one nature: iron is the earth’s own metal, and a magnet is simply a noble iron ore. The earth’s magnetic force, acting through the whole mass of the globe, produces verticity—a directing vigor—in magnetic bodies, and bodies most like the earth, loadstone and iron, are ruled and controlled by this effluence.
Gilbert builds the case by experiment. He shapes loadstones into spheres, which he calls terrellas, and maps their poles, equators, meridians, and spheres of influence as though charting a small planet. He distinguishes magnetic coition from electric attraction, coins the vocabulary of electric force and electric emanations, and insists throughout that his hypotheses be judged by demonstrations rather than by the weight of Greek opinion. He openly expects resistance: his doctrine, he writes, contradicts most received principles, and he refuses to dress it in rhetorical ornament or to cite the ancients as proof.
Inside the Book
Front Matter and the Translator’s Task
The volume opens with its title pages: the 1893 English edition naming William Gilbert of Colchester, “Physician of London,” and the Latin original of 1600, printed by Petrus Short, its epigraph declaring that electrics attract in the same way as amber. P. Fleury Mottelay’s preface explains that he began translating in 1889, was delayed by his own chronological history of electricity and magnetism, and found the work unusually hard—Gilbert coined new words and kept medieval scholastic terms no substitute can replace. Forma joined to materia makes a thing’s true nature; the earth is informed with verticity, and to lose it is to be deformate. Quoting Dryden on translation’s difficulty, Mottelay admits he worked with latitude, sense before words.
The Life of Gilbert
The biographical memoir traces Gilbert’s rise: born at Colchester in 1540, educated at St. John’s College, Cambridge, where he took his M.D. in 1569, then Fellow and eventually President of the College of Physicians. Elizabeth made him physician-in-ordinary and granted him a pension. His early chemical studies gave way to electricity and magnetism, and after eighteen years he published De Magnete in 1600. Hallam praised it; Galileo was drawn by it to study magnetism; Bacon slighted its theory. Cooke noted it had never been Englished despite demand reaching back to 1618. Gilbert coined “electric force” and “electric attraction,” named the magnetic poles, and shaped loadstone into a terrella, a little earth. He invented the versorium and two instruments for finding latitude at sea. He died in 1603, unmarried, buried at Holy Trinity, Colchester; his books and instruments went to the College of Physicians and burned in the Great Fire.
Barlowe, the Appendix, and the Missing Manuscript
A letter from Gilbert to William Barlowe thanks him for his diligence and for finding “dinars good secrets,” urges him to go on double-capping his loadstone, and promises to commend him to Lord Effingham. A Venetian secretary brought greetings from Johannes Franciscus Sagredus, a great magnetic man who had conferred with the learned of Venice and Padua and reported their liking for Gilbert’s book. Gilbert proposes an appendix of six or eight sheets with new inventions, asking for Barlowe’s experiments to appear under Barlowe’s own name—an appendix, the memoir notes, never printed. Silvanus Thompson found no line of Gilbert’s hand save a doubtful inscription, though a presentation copy inscribed to John Sherwood survives. Fuller wrote that Gilbert’s memory, unlike Mahomet’s tomb, will never fall; Dryden predicted Gilbert shall live till loadstones cease to draw.
Edward Wright’s Address
Edward Wright’s laudatory address argues that no subject could be more useful than the loadstone, by whose God-given favor vast continents and nations hidden for centuries were discovered, the globe circumnavigated by Drake and Cavendish, and the magnetized needle made a sure guide—a “God Mercury”—in murky sky and deepest night. The pointer’s variation, constant in each place, lets mariners find their position; the Portuguese approaching the Cape of Good Hope read it as their surest token. The ancient problem of longitude seems near solution, provided latitude is known. Yet variation needs sun or stars—so the dipping needle, touched by the loadstone, shows true direction in darkness and, in London’s latitude, dips nearly seventy-two degrees.
The Author’s Preface and Explanation of Terms
Gilbert marks discoveries with asterisks by importance, warns experimenters to work deftly rather than heedlessly, and concedes his hypotheses will clash with received opinion. His philosophy is almost new; he cites no Greek authorities, since Greek argument cannot demonstrate truth more subtly. He avoids rhetorical ornament, coining new words not to veil things but to publish them plainly. The terms are then defined: terrella, verticity, electrics, the excited and non-magnetized versorium, the armed loadstone, cuspis and crotch, sphere of influence and of coition, ostensio, magnetic coition—preferred to attraction because the two bodies come together harmoniously—and the declinatorium.
Book First: Ancient Errors and the Kinds of Loadstone
Book First surveys the old writings. Early philosophy was rude; the loadstone, likely found by iron-smelters, showed its attraction plainly, yet the ancients recorded little beyond it, appending fables: that garlic or a diamond destroys the power, that Mahomet’s shrine hung by magnets. Pliny tells of Chinocrates’ unfinished arched roof at Alexandria. Cardan berated others yet added nothing. Later authors dwelt only on medicine. The stone’s names come from Magnesia, from Hercules, from sideritis; Egyptians called it the bone of Horus. Differences among loadstones rest on power—male and female, the five sorts of Sotacus, colors from red to white and blue-black, heavy and light, firm and friable, some lifting many times their weight, others barely a fragment.
The Origin of Metals and the Nature of Iron Ore
Gilbert rejects the notion that fresh water, quicksilver, sulphur, or unctuous bodies serve as the principles of metals. These are not causes but results of another natural process. The earth gives forth humors not from water or dry earth but from its own matter, and humors arise from sublimed vapors originating in the earth’s bowels. Aristotle is partly right: exhalations condensing in the earth’s veins are the prime matter of metals, coalescing with solid matter in temperate cavities as a seed grows in the warm uterus. Some metals are obtained pure and need no smelting; others mixed with foreign earths must be smelted. Metals take their perfecting forms from universal nature when earth cavities and the conformation of ground concur with fit matter—not from any planetary influence, as simpletons and raving astrologers imagine. The proximate cause is the fluid from exhalations, like blood and semen in animals, which enters bodies, changes them into marchasites, and forms metals. Iron and loadstone—nothing but a noble iron ore—result when exhalations enter interior homogeneous matter. Nature seldom mingles other metals with iron.
Gilbert then examines iron’s matter in the ore rather than smelted metal. Nearly pure iron ore is mined in Ireland, where the smith forges implements without a furnace. In Sussex, England, rich ores of dark and pale ashy color turn liver-colored when heated. Liver-like ore mixed with perfect loadstone yields the best iron. The stone smiris, or emery, is of iron, though smelted from it with difficulty, and attracts an unmagnetized needle. Thomas Erastus reports iron ores resembling metallic iron but soft and greasy, mouldable like butter; Gilbert has seen similar ores in England resembling Spanish soap. Besides stony ores, iron is deposited from ferriferous water and obtained from sandstones and clayey stones that appear to contain more sand or marl than iron.
The Medicinal Power of Iron
Iron benefits many diseases through virtues both natural and acquired by skilful preparation. The best iron—stomoma, chalybs, or steel—is filed to fine powder, treated repeatedly with strongest vinegar, dried in the sun, washed in spring water, pulverized on porphyry, and sifted. It is given chiefly for lax and over-humid liver and tumid spleen after suitable evacuations; pale, muddy young women are restored to soundness and comeliness. Some prescribe it for obstructions of liver and spleen, and hence in dropsy, schirrus of the liver, chronic jaundice, and hypochondriac melancholia, often to patients’ destruction. Fallopius recommends his own iron preparation for schirrus of the spleen but is much mistaken: loadstone helps a lax, humor-swollen spleen yet worsens a schirrous one. Some burn iron until red, calling it “saffron of Mars,” a powerful exsiccant penetrating the intestines. Steel preparation is indicated for tumid spleen; chalybeate waters reduce the spleen, though iron is generally of frigid efficiency and constringent rather than resolvent—not by heat or cold but by its own dryness mixed with a penetrant fluid. But if the liver is indurated through age or the spleen dried into schirrhus, steel hastens death. Whether iron is warm or cold is disputed; Gilbert mocks sciolists wrangling and confusing learners. Avicenna says iron filings produce intestinal pains and marasmus, but mistakenly declares the antidote to be a drachm of loadstone in a draught of dog’s mercury—for loadstone is often injurious and fatal, does not withstand iron, and cannot attract when drunk as powder.
Amber, Jet, and the Nature of Electrical Attraction
Gilbert disputes Scaliger’s etymology of amber, noting that in Arabic carab means oblation, not “snatching chaff.” The Latin succinum derives from succus (juice). Amber mostly comes from the sea, gathered on coasts after storms by peasants such as the Sudini of Prussia. It seems produced deep in the earth like other bitumens, then washed out and hardened by sea-waves, forever enclosing visible flies and grubs. Ancients and moderns report that amber attracts straws and chaff; jet, a hard black bitumen concretion, does the same. Many modern authors write of this attraction but offer no experimental proof, dealing only in esoteric, mystical words bearing no fruit. Not only amber and jet attract light corpuscles: so do diamond, sapphire, carbuncle, opal, amethyst, beryl, rock crystal, glass, artificial gems, antimony glass, fluor-spars, belemnites, sulphur, mastich, sealing-wax, hard resin, orpiment, and—in dry air—sal gemma, mica, and rock alum. These electrics attract not only straws and chaff but all metals, wood, leaves, stones, earths, water, and oil.
To understand this, Gilbert instructs making a rotating-needle (versorium) of metal, three or four fingers long, poised on a sharp point; bringing rubbed amber near one end makes it revolve. Galen recognized three kinds of attraction, but this division cannot define the causes of amber, jet, diamond, or loadstone. Amber does not attract by heat: heated or burning, it does not attract. Cardan and Pictorius compare it to a cupping-glass, but that force is not igneous. Lucretius’s displaced-air cause fails. In open air, heated objects—white-hot iron, flame, candle, torch, red-hot coal—do not attract straws or the versorium. Amber’s force is not a peculiar property or special relation, since many substances show it and attract all bodies. Likeness is not the cause, since similar and dissimilar things alike are attracted.
The Magnetic Chain and the Errors of the Ancients
Gilbert opens this stretch by asking how magnetic energy actually inheres in iron and loadstone. When iron nails form an unbroken line, a loadstone raises the magnetic form of the objects nearest it, turning them into auxiliary forces that pass the power onward down the chain—though each link seizes the next less powerfully than it was seized itself. Iron takes this force from mere contact, or even from the stone’s presence at a distance, and keeps it. Against Themistius of Paphlagonia, Gilbert insists iron does not hold these powers only while a loadstone sits nearby. The best steel is solicited from farther off, lifts more, and holds more firmly than cheap iron. Fracastorio’s claim that a loadstone attracts loadstone on one side and iron on another he dismisses as plain mal-observation: properly situated and free, a loadstone attracts both.
The Ordering of Energy in Magnetic Bodies
How is that energy ordered? A magnetic body unites forcibly with a strong stone, feebly with a defective one, and a loadstone does not attract equally at every point. On a terrella the poles show the rarest energy; at the equinoctial line no force attracts the ends of magnetic objects, though directive force there is strong. Energy increases poleward by confluence, and the pole is the throne where the whole plane’s force gathers. Cut the stone in two and each half keeps its own poles, verticity is not reversed—here Gilbert corrects Baptista Porta—and no single part holds supereminent value, each being what it is through its neighbors.
Coition, the Sphere of Influence, and Magnetic Circles
Separate bodies cohere by another movement when free, tending toward the stone obliquely near the equator and directly at the poles. The force is given out in all directions, spherically around a terrella, unevenly around irregular shapes, and its sphere does not persist: the loadstone excites magnetic bodies at a convenient distance, its act subtler than light, unhindered by dense or opaque bodies, seizing what stands in amicable relation to it. Gilbert then turns to magnetic circles and limits, accepting natural bounds set in the terrella and earth rather than imaginary lines, and begins tracing meridians from pole to pole.
Iron-Filings, Heat, and the Bond of the Earth
Iron pieces near a loadstone come together eagerly even without contact, and iron dust packed in paper tubes coalesces into one mass that acts like a continuous rod, taking north-south direction, then separates again at a distance. From this Gilbert draws a large conclusion: the foundations of the earth are conjoined and held together magnetically, so Ptolemy and others need not fear the globe will fly apart. Heat weakens the power—roasted filings become Crocus Martis and are not attracted at all, and a loadstone subjected to great heat loses its humor and its nature.
Nutrition, Restoration, and the Cooperation of Stones
Against Cardan and Alexander Aphrodiseus, Gilbert denies that iron nourishes the loadstone; Porta’s buried stone gained only superficial dust. No charlatanry of Paracelsus, dipping a half-candescified stone in oil of vitriol, can increase its force—such a stone loses what it had. Yet a stone rubbed with steel improves, and a strong loadstone can strengthen another, its pole raising iron to the perpendicular while the weaker stone cannot. Weaker stones are refreshed by stronger ones, and there is mutual love and undying good-will among magnetic parts.
Testing Stones and the Fables of Attraction
Strength is judged by the mass lifted, by readiness of turning, and by a versorium held at distance; Porta’s balance-and-sand method, learned from Cardinal Cusanus, weighs a stone’s force. Iron ore is tested by roasting, crushing, and drawing the dust out with a loadstone. Gilbert then sweeps away vulgar errors: the diamond does not pull iron from a loadstone, no loadstone attracts gold or silver, Cardan’s flesh-attracting magnes is absurd, and the remora, the sagda, and Pliny’s glass-attracting loadstone are fables or misreadings. A red-hot loadstone attracts nothing; strong heat destroys its power.
Verticity, Direction, and the Iron of Rimini
Iron stripped of magnetic form by heat wanders without fixed direction but may slowly regain feeble verticity from the earth, while a burnt loadstone cannot be restored. Rubbing one end of a wire magnetizes the whole mass instantly, and iron touched on a stone’s north side turns to earth’s north, not south, because iron and loadstone become one body when joined. Cutting a magnetized needle preserves direction; needles transmit force onward in succession. Verticity exists in all smelted iron: a smith facing north hammers bars that then point north, bars in buildings acquire it over twenty years, and Master Philip Costa writes of iron at Rimini’s Church of San Agostino that turned to the loadstone after long polar alignment.
Why Only Magnetic Bodies Take Verticity
Gilbert presses the argument that the earth’s magnetic force, working through the whole mass of the globe, produces verticity in magnetic bodies, and that those most like the earth—loadstone and iron—are ruled by this effluence. Iron returning from heat to its natural temperature resembles a newborn drawing qualities from the planets; long bars sometimes take the same verticity at both ends and waver, as when a four-foot iron wire is rubbed at both ends with one pole of a loadstone. Chapter XIII asks why friction with a loadstone grants verticity only to magnetic bodies. Wood, gold, silver, copper, zinc, lead, and glass, floated on cork, never turn surely to the world’s poles, and rubbed with loadstone show neither poles nor variation, lacking primary qualities and mixed with efflorescent humors. Iron’s primal properties wake at the loadstone’s approach like animals from sleep. Gilbert refutes Baptista Porta, who claimed iron rubbed with diamond turns north: he tested seventy-five diamonds before many witnesses, using bars and wire floated on corks, and never saw the effect. Porta was misled by the iron’s own verticity from the earth; diamond, sometimes called siderite for its glister, does not attract iron.
Poles and Centre Shift When a Stone Is Cut
Chapter XIV corrects Porta’s error that a loadstone or iron suspended in equilibrium reverses when a second stone or iron is applied beneath; the ends always turn to the same points. Porta wrongly inferred east, west, superior, and inferior poles. Chapter XV explains that poles, equator, and centre are permanent in an unbroken loadstone but shift when it is reduced. Cutting a terrella along the Arctic circle moves the pole from A to I while centre and equinoctial circle recede toward B; cutting from the side moves poles and axis from AB to EF. These points migrate because verticity is no fixed part but a tendency of force from the whole; rejoined in natural position, the terminals return, and every minutest piece, even magnetic gravel and sand, forms a new whole. Chapter XVI adds that breaking off the south part reduces power in the north, since the opposite part formerly increased mass, verticity, and force toward unition.
Rotary Needles and the Mariner’s Compass
Chapter XVII treats rotary needles. Magnetized versoriums recognize rich iron ores, magnetic stones, clays, and earths; the mariner’s compass has carried Spaniards and Englishmen round the globe; needles find iron veins, drive mines in sieges, train cannons at night, aid topography and underground aqueducts. Gilbert advises clean, rust-free steel, a dry wiped stone, gentle scraping with polished iron, naked iron on naked stone. He diagrams modes of application: A best, B and C passable, D worse, E bad, L on the equator valueless, G and H bad. Conical stones with steel caps are used; the stone should be large and strong, the versorium thick with a moderate point. Long needles may dip after friction, so the north end should be slightly lighter beforehand; afterward keep the versorium boxed away from other magnetic bodies. Rubbing both ends at opposite poles increases steadiness. Iron keeps power for centuries if laid meridionally, not on a parallel, and not rusted. Gilbert disputes Porta’s ratio between loadstone and iron: a small iron mass takes full virtue though the stone weigh over 100 lbs. Porta wrongly thought energy passed by adhesion of loadstone particles like hairs; these are merely scrapings. Strokes should terminate at one end; ending at the middle excites little or no verticity. In northern latitudes the stone’s true north pole faces the zenith, rubbing the end that will turn north; in southern latitudes the case differs, explained in Book II, Chapter 34. A versorium rubbed between two equal conjoined loadstones acquires nothing; if unequal, force comes from the stronger. Begin at the middle, draw so one end quits last, continue gently one or two minutes, and do not repeat the middle-to-end movement. An armed stone lifts more iron but does not magnetize more powerfully than an unarmed one; equal wires excited by armed and unarmed ends move at the same distances. Strongly excited objects turn quickly, feeble ones slowly and only when nearer, tested in water with equal corks.
Variation Enters the Argument
Book IV, Chapter I turns to variation. Direction had been treated as if no variation existed, as in a perfect sphere, but earth’s magnetic direction departs from the meridian; earlier writers recognized no difference between direction and variation. True direction is motion to the true meridian with ends pointing to the respective poles; variation is deflection toward a point near the meridian, an arc of the horizon between the meridian’s intersection and the deflection’s term, varying by locality. Its terminus is assigned to a circle of variation and a magnetic meridian through the zenith and the point of variation. In northern latitudes variation runs from north toward east or west; in southern, from south toward east or west. Navigators err by noting only the north point on both sides of the equator. Earth is the cause of variation. Gilbert rejects the common opinion of magnetic mountains or a distant phantom pole, adopted by Fracastorio.
The Arc Does Not Grow with Distance
Chapter IV argues the arc of variation does not change proportionally with distance. A ship sailing the same parallel from the Scilly Islands toward Newfoundland, after reaching the point where the compass points to the true magnetic pole, begins to show variation faintly, which then increases at a higher ratio over equal distances until nearing the continent, where variation becomes very great; but before reaching port, at some distance, the arc lessens slightly. Departing from that parallel north or south changes variation according to land position and latitude; other things equal, higher latitude means greater variation.
Islands and Mines Do Not Alter Variation
Chapter V holds that ocean islands do not alter variation, nor do loadstone mines.
The Case Against the Primum Mobile
Gilbert finds it improbable that the highest heaven and the fixed stars are swept around in a rapid headlong career. No genius has located the fixed stars within a single Ptolemaic sphere, nor given rational proof of adamantine spheres. The planets lie at various distances from earth, and the fixed stars are likewise ranged at various heights; they are not set in any sphaeric framework or vaulted structure. The imagined intervals between spheres are speculation, not fact. Astronomers have observed 1022 stars, with innumerable others appearing minute or hardly discernible save by the keenest eye. The space between us and the remotest fixed stars is inconceivably great, beyond eye, man’s devices, or thought. Gilbert calls the motion of spheres an absurdity.
All heavenly bodies, he holds, are set in destined places, conglobed with their elements and parts. If they have motion, it is either round their proper centre, like the earth’s rotation, or a progression in an orbit, like the moon’s. In so multitudinous a scattered flock there is no circular motion. Stars near the equator would seem borne around most rapidly, those near the pole less rapidly, and others almost motionless; yet no differences in light, mass, or color are perceptible. They remain in their seats, not suspended, fastened, or secured in any vault.
The primum mobile Gilbert calls far more extravagant—a fiction believed by some philosophers and accepted by weaklings. It presents no visible body and is in no wise recognizable. There cannot be diurnal motion of infinity or of an infinite body, nor of this immeasurable primum mobile. The moon circuits in twenty-seven days; Mercury and Venus move tardily; Mars completes his period in two years, Jupiter in twelve, Saturn in thirty. Astronomers ascribe motion to the fixed stars completed, according to Ptolemy, in 36,000 years, or, according to Copernicus’s observations, in 25,816 years. In larger circles motion is ever more slow, yet the primum mobile has a diurnal revolution. Gilbert calls this superstition, a philosophic fable believed only by simpletons and the unlearned, beneath derision, though once supported by calculation and accepted by mathematicians, egged on by philophasters.
The motions of the planets seem eastward, according to the zodiacal signs; mathematicians and vulgar philosophers believe the fixed stars progress the same way slowly, adding a ninth sphere through ignorance. The primum mobile must wheel from east to west, counter to the rest of the universe. Whatever moves naturally is impelled by its own forces and by consentient compact of other bodies—the motion of parts to a whole, of globes and stars accordant, the circular propulsion of planets observing and inciting each other’s career. But where are the bodies that incite or propel the primum mobile? What mad force lies beyond it? Agent force abides in bodies themselves, not in space or interspaces.
Gilbert compares one who supposes bodies idle and all force in spheres to a fool who thinks ceilings and floors govern a household rather than the provident good-man. Not by the firmament are stars borne; far less are they whirled by the primum mobile in reversed direction at highest velocity.
Ptolemy of Alexandria seemed over-timid in fearing a break-up of the nether world were earth to move in a circle. Gilbert asks why Ptolemy does not apprehend universal ruin, dissolution, confusion, conflagration, and stupendous calamities from a motion surpassing all imagination. We are borne round by the earth’s daily rotation—a more congruous motion; as a boat glides over water, so are we whirled with the earth while thinking we stand still. This seems wonderful to some philosophers because of ingrained belief that the earth’s mighty mass makes an orbital movement in twenty-four hours. It were more incredible that the moon, sun, Mars, Jupiter, Saturn, or the fixed stars and firmament should traverse their courses in that time. It is absurd to imagine a primum mobile and give it a motion completed in twenty-four hours while denying that motion to the earth. A great circle of earth compared to the circuit of the primum mobile is less than a stadium to the whole earth. If earth’s rotation seems headlong, worse than insane is the primum mobile‘s motion, in harmony with no other.
Ptolemy and the Peripatetics think all nature would be thrown into confusion and the globe destroyed by earth’s rapid rotation. The earth’s diameter is 1718 German miles; the new moon’s greatest elongation is 65, least 55, semi-diameters of earth; the sun at greatest eccentricity is distant 1142 semi-diameters; Mars, Jupiter, Saturn are farther. The best mathematicians regard the fixed stars’ distances as indeterminable. The primum mobile, if fairly estimated, must travel in one hour as much space as might be comprised within three thousand great circles of the earth; on the firmament’s convexity it would travel over more than eighteen hundred such circles. No structure of iron could withstand such mad velocity. The Chaldees believed the heavens light; but in light there is no such firmness, neither in the fire-firmament of Plotinus, nor in the fluid or watery heavens of Moses, nor in the tenuous transparent firmament between our eye and the stars’ lights. We must reject the deep-seated error about this mad, furious velocity and forceful retardation.
The Magnetic Cause of Rotation
These final chapters argue that the earth’s diurnal rotation is caused by its magnetic form, which Gilbert calls astral—whether energy or soul. He rejects the Stoic notion that the earth is an animal, and mocks Joannes Costeus and the philosophasters for failing to appreciate this grand fact of nature.
Key Ideas
The terrella is Gilbert’s master instrument: a spherical loadstone that reproduces, in miniature, the behavior of the earth. On it he locates poles where the force is strongest, an equinoctial line where it is weakest, and meridians along which iron bars cohere. He defines verticity as an innate turning vigor rather than a rotation, and he treats the magnetic force as something given out in all directions, acting instantly within its limits and passing through dense or opaque bodies that would stop light.
His vocabulary is deliberately new. He prefers coition to attraction, because magnetic movements are two bodies coming together in harmony rather than one tyrannically drawing the other. He describes the armed loadstone—one fitted with an iron helmet or cap—and argues that arming concentrates rather than increases its native power. He names the versorium, the pivoted needle that became the basis of electrical experiment, and the declinatorium, the vertically moving needle used to measure the dip. He also draws a firm line between magnetic and electric bodies: amber, jet, glass, and gems attract light matter by effluvia generated from humor, while loadstone and iron act by a formal efficiency proper to the earth.
The book’s practical reach is inseparable from its theory. Gilbert credits Robert Norman with first discovering the dip of the magnetic needle, and he treats variation—the needle’s deviation from true north—as a navigational problem of the first order. Edward Wright’s prefatory address spells out the stakes: by the magnetized needle, north, south, east, and west are known to sailors even under murky skies, and the Portuguese on the route to the East Indies read their approach to the Cape of Good Hope in the needle’s changing variation. The ancient problem of finding longitude, Wright suggests, is on its way to solution.
Themes
The book is a manifesto for a new way of knowing. Gilbert’s preface asks readers to handle bodies carefully and deftly, to repeat his experiments rather than condemn them from ignorance, and to accept that certitude in magnetic philosophy requires knowing all or most of its principles. He grants Aristotle, Theophrastus, Ptolemy, Hippocrates, and Galen their due, then notes that this age has discovered many things they would gladly have adopted. The break with the schools is explicit: he rejects the four-elements explanations, the astrological assignment of metals to planets, and the habit of copying fables from author to author.
That polemic against inherited error runs through the whole work. Gilbert traces the garlic-and-diamond stories to Pliny and Ptolemy’s Quadripartitum, notes that even Agricola repeated them as history, and dismantles the tale of Mahomet’s suspended shrine. He is equally impatient with contemporaries: Cardan’s loadstone that unearths buried silver, Porta’s loadstone fed on iron filings, Paracelsus’s recipe for multiplying a stone’s force tenfold by dipping it in oil of vitriol. Against all of this he sets the plain test—which stone turns a needle from the greatest distance, which lifts the greater weight.
There is also a cosmological ambition underneath the experiments. If the earth is a magnet, then its parts are held together magnetically, and the old fear that a spinning earth would fly to pieces loses its force. Gilbert compares the mutual attraction of loadstones to love and undying good-will, and speaks of the earth’s globe cohering electrically while it revolves magnetically. The little terrella on the bench is meant to be the world in miniature, and the laws he reads off it are meant to be the laws of the planet.
Why It Matters
Gilbert’s contemporaries recognized the book as something new. Robison called it the first-fruits of the Baconian or experimental philosophy; Galileo admired it and was drawn by it to study magnetism; Sarpi named Gilbert, with Vieta, the only original writer of his age. He gave the language its words for electric force, electric attraction, and the magnetic poles, and his versorium opened the line of inquiry that later experimenters would follow.
The book also had a long afterlife as an object. It went untranslated into English for centuries despite demand as far back as 1618, when William Barlowe was already urging the need; the 1600 original became a collector’s prize, and a presentation copy inscribed by Gilbert’s own hand survives. Gilbert died in 1603, before the appendix of new inventions he promised Barlowe ever reached print, and the books and instruments he left to the College of Physicians burned in the London fire of 1666. What remains is the treatise itself, and the habit of mind it argued for: trust the experiment, repeat it, and let the stone answer for itself.
