This is a foundational scientific treatise from the year 1600, written in Latin by an English physician and natural philosopher. It sets out to demonstrate, through hundreds of experiments, that the earth itself is a giant magnet and that the loadstone’s powers are not occult marvels but natural effects governed by laws that can be observed, measured, and repeated. The work is arranged in six books, moving from the nature and properties of the loadstone and iron, through magnetic movements, direction, variation, and dip, to the culminating claim that the terrestrial globe is magnetic and is itself a great loadstone.
“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 magnetism is not a curiosity of a single rare stone but the governing principle of the earth’s own body. The loadstone and iron are, he argues, the same substance in different states, generated together in the earth’s veins and differing only in purity and coherence. From this identity he builds outward: if iron and loadstone share one nature, and if the earth produces both and is held together by the same force, then the earth must be magnetic through and through. The daily rotation of the earth, the steady pointing of the compass, the slow drift of variation, and the downward dip of the needle all follow from this one fact.
What makes the argument distinctive is its method. Gilbert refuses to reason from Greek authorities or from the four elements and prime qualities of the schools. He insists on experiment first, and he marks his experiments with asterisks according to their importance and subtlety, warning readers that a failed trial usually means a clumsy hand rather than a false discovery. He coins new terms where the old vocabulary fails him, and he says plainly that his philosophy is almost new and unheard-of, at variance with most received opinion. He does not expect to be believed at once; he expects the demonstrations themselves to win authority in time.
Inside the Book
The 1893 Mottelay Edition and Its Prefatory Matter
The volume opens with the apparatus of a nineteenth-century scholarly edition: the 1893 New York printing by John Wiley & Sons, P. Fleury Mottelay’s translation, and a reproduction of the Latin title page of the 1600 London original, which names Gilbert as a Colchester man and London physician and calls the work a “new physiology” proved by arguments and experiments. Mottelay explains that he began translating in 1889, was delayed by his own history of electricity and magnetism, and aimed at idiomatic English rather than literal substitution, thanking a long list of scientific and literary friends. He warns that Gilbert coined words and kept scholastic terms—forma joined to materia makes a thing’s nature, the earth is “informed with verticity,” and iron can be deformated or reformated—and admits he translated with latitude, following sense over words.
The Biographical Memoir
The memoir traces Gilbert (or Gilberd), born at Colchester in 1540, through the local grammar school to St. John’s College, Cambridge, where he took his degrees and became a fellow and mathematical examiner, then traveled abroad and rose in the Royal College of Physicians to its presidency in 1600, serving as physician to Queen Elizabeth. His early chemistry gave way to electricity and magnetism, dormant since Thales, and De Magnete appeared in 1600 after eighteen years’ work. The memoir gathers testimony from Hallam, Galileo, Bacon, and others, credits Gilbert with the terms “electric force” and “magnetic poles,” with the versorium and two navigational instruments, and with shaping a loadstone into a terrella. It records his death on 30 November 1603, his burial at Holy Trinity, Colchester, his unmarried life, his books left to the College of Physicians and burned in 1666, and the posthumous De Mundo of 1651.
Barlowe, the Lost Appendix, and Gilbert’s Hand
A letter from Gilbert to William Barlowe thanks him for his diligence, urges him to proceed with “double capping” his loadstone, promises commendation to Lord Effingham, and mentions a Venetian secretary who brought a Latin letter from the magnetical man Sagredus. Gilbert proposes an appendix of six or eight sheets with new inventions, including some of Barlowe’s experiments under his own name—but the memoir notes it was never printed. Silvanus Thompson found no certain line of Gilbert’s handwriting, save a doubtful inscription and a possible signature on a 1596 petition of the College of Physicians; the British Museum manuscript of De Mundo is probably not his, since the Elzevir print says the original was partly English. A 1600 presentation copy inscribed to John Sherwood passed through Quaritch’s hands, Fuller likened Gilbert’s memory to Mahomet’s tomb upheld by De Magnete, and Dryden predicted he would live till loadstones cease to draw.
Edward Wright’s Address and the Author’s Preface
Edward Wright defends Gilbert against disparagers, praising the loadstone’s role in discovering continents and in the circumnavigations of Drake and Cavendish, the needle’s guidance through murky nights, and variation as a sign of distance on voyages to the Cape of Good Hope and from the Gulf of Mexico to the Azores. He notes that dip, nearly seventy-two degrees at London, might give latitude in the darkest night, calls Gilbert his master, and argues for the earth’s diurnal rotation over a primum mobile, addressing Scripture and citing Plantius and Stevinus. Gilbert’s own preface prefers sure experiments to conjecture, begins with common magnetic matter to penetrate the earth’s inner parts, compares his method to geometry, laments the ocean of books, and dedicates his new style of philosophizing to true philosophers, noting his many experiments, pains, sleepless nights, and expense.
The Explanation of Terms
A glossary fixes the vocabulary: terrella for a spherical loadstone; verticity for polar turning power, an innate directing vigor rather than revolution; electrics for bodies that attract like amber; excited for iron or steel that acquires magnetism; the versorium as a needle on a point; the armed loadstone as one capped with iron; meridionally and paralleletically for directions; cuspis for the end of a magnetized versorium; crotch for the untouched end; radius and sphere of influence and sphere of coition for the geometry of magnetic action; ostensio for physical demonstration; coition rather than attraction, since magnetic movement joins two bodies harmoniously; and declinatorium for the dipping needle.
Book First, Chapter I: The Loadstone Found and Named
Philosophy in rude ages knew few properties of things, and mineralogy lay neglected until men searched forests, mountains, and the inmost bowels of earth. The loadstone, Gilbert supposes, was found by iron-smelters in veins of iron ore, and once treated it showed a strong attraction of iron—no obscure property but one seen of all. Ancient philosophers and physicians discoursed of it briefly: Plato in the Io, Aristotle in the first book De Anima, Theophrastus, Dioscorides, Pliny, Solinus. Whewell lists the English observers of variation—Hariot, Hues, Wright, Kendall—and the instrument-makers Borough, Barlo, and Robert Norman, the good seaman who first discovered the dip in 1576.
Names, Kinds, and Virtues of the Loadstone
The stone’s name is variously derived: from a region where a shepherd’s cattle were held fast, from Magnesia in Macedonia, or from Magnesia in Ionia on the Maender; Lucretius says the Greeks call it Magnes from its country.
The Origin of Metals and the Nature of Iron Ore
Fresh water, Gilbert insists, is no element but a thinner consistence of the earth’s own evaporated fluids. The unctuous bodies, the propertyless water, quicksilver, and sulphur that the chemists make principles of metals are themselves products of a deeper process. Humors rise as sublimed vapors from the earth’s bowels; all waters are extractions and exudations from the earth, which is no simple substance as the Peripatetics imagine. Aristotle is partly right: exhalation condensing in the earth’s veins is the prime matter of metals. Condensed in cooler wombs shaped by lands and mountains, it changes into metal, coalescing with solider matter, sometimes yielding pure metal that needs no smelting, sometimes mixed with foreign earths that must be fired. Metals arise not from any proportion of matter or specific virtues, as the chemists dream, but when cavities and conformation of ground concur with fit matter. Their variety is small, hardly ten; the raving astrologers who refer them to planets find no agreement in number or property—what has Mars to do with iron, Venus with copper? Exhalations are the remote cause; the proximate cause is the fluid from them, like blood and semen in animals, entering bodies and turning them to marchasites, then to veins, then to metals in their matrices. Oftenest it enters homogeneous matter and yields a vein of iron—or loadstone, which is nothing but a noble iron ore. Nature seldom mingles other metals with iron. Deep in the globe lie hidden the principles of metals and stones, as at the surface lie those of herbs; earth from a deep pit strewn on a tower brings forth green herbage, and each region produces its own. What chemists call fixed earthy sulphur in iron is the homogenic matter of the globe held by its own humor and hardened by a second. It is wrongly said that gold holds pure earth and iron impure; in iron, especially the best, is earth in its true and genuine nature, while other metals hold rather condensed fixed salts, efflorescences of the Earth. Having declared the origin of metals, Gilbert turns to the matter of iron in the ore. Iron appearing pure is found in the earth, yet not exactly metallic iron—sometimes coated with a white moss-like substance, often in river sands, as in the ore of Noricum, the region south of the Danube watered by the Inn and the Drave, mostly comprised in modern Austria. Nearly pure ore is mined in Ireland, from which the smith forges implements without furnace labor. From liver-colored ore France obtains iron with bright scales; England makes it without scales, and carpenters use it instead of chalk. Sussex yields a rich dark ore and a pale ashy one, both turning liver-colored when heated; Sussex too yields a dark ore in square masses with a black rind. The liver-like ore is often mixed with other stones and with perfect loadstone, which yields the best iron. There is rust-colored ore, lead-colored ore mixed with black, simply black ore, black mixed with cobalt, ore admixed with pyrites or sterile plumbago; one kind resembles jet, another the stone haematites. The emery used by glass workers is of iron, though smelted from it with difficulty, and it attracts an unmagnetized needle; it is often found in deep silver and iron mines. Thomas Erastus reports ores resembling metallic iron in color but soft and greasy, mouldable with the fingers like butter; Gilbert has seen the like in England, resembling Spanish soap. Besides numberless stony ores, there is a substance like iron rust deposited from ferriferous water, got from mud, loam, and ochre. In England much iron is obtained from sandstones and clayey stones that seem to contain more sand and marl than iron. Aristotle’s book of wonderful narrations tells that the iron of the Chalybes and the Myseni is carried in the gravel of streams, washed and smelted in the furnace.
The Medicinal Power of Iron
Iron benefits many human diseases, and skilful preparation brings wonderful changes to the body. The best iron—stomoma, chalybs, steel—is filed to powder, treated repeatedly with strong vinegar, dried in the sun, washed in spring water, pulverized on porphyry, sifted, and kept. It is given chiefly for a lax, over-humid liver and a tumid spleen after suitable evacuations; pale, blotchy young women are restored to soundness and comeliness, since it is highly exsiccative and harmlessly astringent. Some, following Arabic writers, prescribe it for obstructions of liver and spleen—dropsy, schirrus, chronic jaundice, hypochondriac melancholia—often to the patient’s destruction. Fallopius recommends his own preparation for schirrus of the spleen but is much mistaken: loadstone helps a lax, tumid spleen yet worsens a schirrous one, since strongly siccative, humor-absorbing agents harden viscera almost to stone. Iron dried in an oven until red is called saffron of Mars, a powerful exsiccant penetrating the intestines; violent exercise is prescribed so the remedy reaches the affected part. Steel preparations suit a tumid spleen; chalybeate waters reduce it, though iron is of frigid efficiency and constringent rather than resolvent, acting by its own dryness mixed with a penetrant fluid. But in indurated liver or schirrous spleen, with atrophied limbs and watery collections, steel hastens death. Rhazes, in Ad Almansorem, recommends iron slag electuary for a dried-up liver—bad counsel. Whether iron is warm or cold is disputed, Manardus, Curtius, and Fallopius arguing both sides.
The Chain of Magnetic Force and the Question of Ordering
Gilbert opens by tracing how force travels through a line of iron nails: loadstone A raises the magnetic form of nails B and C, making them its auxiliaries, and they in turn conduct power onward to D—though D is seized less powerfully than C is by B. The nails take their force from mere contact and from the stone’s presence without contact, retaining it in their bodies. Iron does not hold these powers only while a loadstone is near, nor merely for a moment, as Themistius of Paphlagonia supposed. Steel, the best iron, is solicited from farther off, lifts more, and acquires greater force than cheap iron from impure ores. Fracastorio’s claim that a bit of loadstone attracts loadstone on one side and iron on another is flatly wrong—the result of mal-observation, since he did not know how to present one stone to another properly. A light object moves more readily than a heavy one, which resists more.
How Energy Is Ordered in Magnetic Bodies
Chapter V asks how energy is ordered. A magnetic body unites forcibly with a powerful loadstone, feebly with a defective one. The stone does not attract equally at every point; it has true poles where its rare energy is most conspicuous. In a terrella, the poles hold the greatest attractive force, while at the equinoctial line no force attracts the ends of magnetic objects, though directive force there is strong. Iron on the equator, pulled in contrary directions, does not cling steadily until it falls to one side. Energy increases poleward by confluence of forces from the equinoctial plane, and absolute verticity is seen at the pole while the stone remains whole. Break the terrella and verticity finds new abiding-places in the separate parts—with change of mass always goes change of verticity. Sever it along the axis and the poles in the severed parts are not the old ones; verticity is not reversed, as Baptista Porta erroneously affirms. The integral mass gives the pole its constant place; the poles are dominant in virtue of the force of the whole, and no part has supereminent value—whatever it is, it is because of adjoining parts, producing a perfect whole. From every point of the equator’s plane energy reaches the periphery and tends to the pole, where this mighty power has its throne.
Coition, Heat, and the Refutation of Fracastorio and Porta
Chapter VI turns to the coition of bodies that cohere naturally. Iron pieces near a loadstone, even without contact, come together and glue themselves; iron dust in paper tubes coalesces instantly into one mass, then acts on a piece of iron as if one continuous rod. Thus the foundations of the earth are magnetically conjoined and held together, so Ptolemy and his followers need not fear the earth will go to pieces. Heated iron-filings are attracted less strongly; a loadstone subjected to great heat loses energy because its humor is dissipated, and Crocus Martis is not attracted at all. Chapter XXIV: iron within the field tends toward the stone’s most energetic points unless hindered; if an obstacle prevents reaching the stone, the iron sticks to the obstacle by a less constant bond. Gilbert rejects Fracastorio’s claim that iron can hang fixed in mid-air, and dismisses Porta’s suspended iron held back by a thread as hardly a brilliant idea. Chapter XXV: loadstones differ greatly in energy, and iron is not attracted as nourishment, contrary to Cardan and Alexander Aphrodiseus. Porta’s burying experiment proves nothing; Paracelsus’s charlatanry of half-candescifying the stone and dipping it in oil of vitriol causes loss, not gain. Rubbing with steel or covering with filings can strengthen a stone, and a strong large loadstone increases another’s power. Chapter XXVI: one loadstone attracts another only at a fixed point; iron, once impressed, is renovated and pursues the loadstone, making captive other iron. A steel cap fitted to a pole lifts greater weights. Chapter XXVII: magnetic rays disperse in a circle, the centre being the centre of the stone, not the pole. Chapter XXVIII: coition is strongest pole-to-pole, utterly enervate at the equinoctial line. Chapter XXIX: stones from the same mine have the same potency, but larger stones show greater force; removing a part loses energy, reuniting it recovers strength. Chapter XXX: oblong iron is more quickly attracted and clings more firmly than spherical or square. Chapter XXXI: oblong stones attract more forcibly when the pole is at the extreme end. Chapter XXXII: equal loadstones come together with equal mutual incitation; coition is more vigorous than repulsion, which is the act of the force ordering in place. A loadstone cut along the meridian yields halves that repel each other.
Testing Stones, Ore, and the Fables of Attraction
A strong loadstone can lift in air an iron mass equal to its own weight; a weak one barely attracts fine wire. For valid experiments, stones must be prepared alike, shaped alike, and of equal size. All are tested with a versorium held at a distance: the stone that makes the needle go round at the greatest distance is best. Porta rightly determines power by weighing in a balance, pouring sand until the stone separates from the iron—an experiment Cardinal Cusanus had already given in his Statica. Stronger stones turn readily toward the poles, propel their floats, and come to rest more speedily. Chapter XXXVII: iron ore is tested by magnetic coition—roasted, crushed, washed, and dried, then the loadstone is thrust among the particles and attracts iron dust, removed by a feather brush into a crucible until nothing remains. If the stone picks up dust readily, the ore is rich; if it rejects it, there is little or no iron.
The Earth’s Effluence and the Limits of Magnetic Sympathy
Gilbert presses his argument that the earth’s magnetic effluence fills its whole sphere of force and alters bodies everywhere, though it rules most strongly those most like itself—loadstone and iron. He defends as not wholly superstitious the old practice of noting a country’s position, its horizon points, and the stars overhead. A babe issuing from the womb gains respiration and animal function; planets and heavenly bodies, by their configuration with horizon and earth, impart special qualities to the newborn. So too a piece of iron, while being wrought and lengthened, is affected by the earth as general cause, and returning from its fiery state to its original temperature becomes imbued with verticity according to its position. Long bars sometimes take the same verticity at both ends, giving wavering, ill-regulated motion—like an iron wire four feet long rubbed at both ends with one same pole.
Why Only Magnetic Bodies Take Verticity
No bodies save the magnetic are imbued with verticity by friction with a loadstone, and no non-magnetic body can impart or awaken that force. Wood floating on water never turns to the world’s poles save by chance; nor do threads of gold, silver, copper, zinc, lead, or glass passed through cork and floated show sure direction. Rubbed with loadstone they show neither poles nor points of variation. Bodies not obedient to the earth are in no wise governed by the loadstone’s touch; its energy has no entrance into their interior, nor are their forms magnetically excited—and even if it entered, it could effect nothing, since such bodies lack primary qualities, being mixed with efflorescent humors and degenerate from the globe’s primal property. Iron’s primal properties, by contrast, are awakened by approach of a loadstone, like brute animals and men awakened from sleep.
Porta’s Error Concerning the Diamond
Gilbert wonders at Baptista Porta’s manifest error. Though Porta rightly rejects the inveterate falsehood of an opposite force, he imparts a falser opinion—that iron rubbed with diamond turns north. Porta writes that rubbing an iron needle on diamond and floating it makes it turn north like iron rubbed on loadstone, perhaps more sluggishly; that the opposite part repels iron like the loadstone’s south end; and that many small iron rods in water stood at equal distances pointing north. Gilbert calls this contrary to magnetic rules and reports his own experiment with seventy-five diamonds before many witnesses, using iron bars and wire floated on corks with greatest care; he never saw Porta’s effect. Porta was misled by the verticity iron gets from the earth; the iron of itself tended to its determinate pole, which Porta, ignorant of this, attributed to the diamond. Gilbert warns searchers of nature against delusion by faultily observed experiments. He notes diamond (adamas) is sometimes called siderite (siderites), not because ferruginous or attracting iron (sideros), but for its glister like shining iron—a brilliance possessed by the finest diamonds; by this confusion of names many effects are credited to diamond that belong to loadstone siderite.
Position Does Not Alter Verticity
A loadstone’s position—now above, anon beneath a magnetic body suspended in equilibrium—alters neither the force nor the verticity of the magnetic body. Gilbert corrects an error lately arisen from Porta’s faulty observation; Porta makes three chapters of it. If a loadstone or iron suspended in equilibrium or floating is attracted or controlled by another iron or loadstone held above it, the stone or iron does not turn opposite when the second is applied beneath; the ends ever turn to the same points, however suspended or mounted on a point to revolve freely. Porta erred through uneven shape of some loadstone or mismanaged experiment. He wrongly inferred that as loadstone has north and south poles, it has also east and west, superior and inferior poles. Thus many vain imaginations arise from mistakes accepted as true judgments.
Poles and Equator Shift When the Stone Is Cut
Poles, equator, and centre are permanent and stable in the unbroken loadstone; when it is reduced and a part taken away, they vary and occupy other positions. Gilbert works geometrically: let AB be a terrella, E its centre, DF its diameter, also its equinoctial circle. Cutting out a piece along the Arctic circle GH, the pole formerly at A now sits at I; centre and equinoctial circle recede toward B, always in the middle of the remaining mass between the plane of Arctic circle GH and Antarctic pole B. The segment between the former equinoctial circle DEF and the newly acquired equator MLN equals half the part cut off, GIHA. If the part be cut from side CD, poles and axis lie not in AB but in EF, the axis changing in the same proportion as the equator previously. These terminals of forces flowing from the entire form move with change of mass or figure; verticity is not innate in a part or fixed point but a tendency of force to such part. As a terrella dug from the earth has its own special poles and equator, so if cut again these points migrate. If the loadstone be divided on parallels or meridians and the cut-off part be set back in natural position and conjoined, though not cemented, the terminal points return as though nothing had been cut away. When the body is whole the form remains whole; when mass is reduced a new whole results, and a new wholeness necessarily arises in each minutest piece, even in magnetic gravel and fine sand.
Variation Differs from Place to Place
Variation is never fixed at a given place but differs from place to place. True polar direction originates in the whole globe but is slightly diverted toward particular eminences of great magnetic force on the broken surface. The arc of variation does not change proportionally with distance: on the ocean, one degree per hundred miles does not imply the same for the next hundred.
The Absurdity of the Primum Mobile
Gilbert turns his attack on the machinery of the schools. That the highest heaven and the visible splendors of the fixed stars should be swept around in a rapid headlong career he finds improbable on its face. No genius ever placed the so-called fixed stars within one same Ptolemaic sphere, nor gave rational proof of adamantine spheres. The planets lie at various distances from earth, and the great luminaries are ranged at various heights and remote distances—not set in any sphaeric framework, firmament, or vaulted structure. The intervals imagined by some authors are speculation, not fact; the real intervals far surpass them. Situated at various distances in thinnest aether, subtile fifth essence, or vacuity, how could the stars keep their places in the swirl of enormous spheres made of an unknown substance?
Astronomers have observed 1022 stars; innumerable others appear minute, and still others are hardly discernible save by the keenest eye. Even the best-sighted, when the moon is below the horizon and the atmosphere clear, will feel there are many more, obscured by distance. What inconceivably great space lies between us and the remotest fixed stars, and what is the vast amplitude of the imaginary sphere supposed to hold them? They are beyond reach of eye, man’s devices, or thought; the motion of spheres he calls an absurdity.
All heavenly bodies, he concludes, are set in their destined places, conglobing whatever elements bear to their own centres, with their parts assembled around them. If they have motion, it is either motion of each round its proper centre, like the earth’s rotation, or progression in an orbit, like the moon’s; in so multitudinous a scattered flock there will be no circular motion. Stars near the equator would seem borne around with greatest rapidity, those nearer the pole less rapidly, and others almost motionless—yet no differences in light, mass, or color are perceptible; they are as brilliant or faint toward the poles as near the equator and zodiac. They remain in their seats, suspended from nothing, fastened in no vault.
Far more extravagant still is the whirling of the supposititious primum mobile, which would have to be of enormous altitude and mass, surpassing all creation below, to make the whole universe down to earth revolve from east to west—implying a universal force, unending despotism, and hateful tyranny in the governance of the stars. This primum mobile presents no visible body and is a fiction accepted by weaklings. There cannot be diurnal motion of infinity or 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, per Ptolemy, in 36,000 years, or per Copernicus’s observations in 25,816 years; in larger circles motion is ever more slow—yet the primum mobile, surpassing all in height, has a diurnal revolution. Gilbert calls this superstition, a philosophic fable believed only by simpletons, beneath derision, though once supported by calculation and accepted by mathematicians while philophasters egged them on.
The motions of the heavenly bodies seem eastward, according to the zodiacal signs; vulgar mathematicians and philosophers believe the fixed stars progress slowly the same way, adding a ninth sphere. 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 a consentient compact of other bodies; but where are the bodies that incite the primum mobile, and what mad force lies beyond it? Agent force abides in bodies, not in space or interspaces. He who supposes all bodies idle and all force in the spheres is as foolish as one who thinks ceilings and floors govern a household rather than the provident good-man.
Ptolemy of Alexandria, Gilbert says, was over-timid in fearing a break-up of the nether world were earth to move in a circle; why not apprehend universal ruin from a motion surpassing all imagination? We are borne round by the earth’s daily rotation—as a boat glides over water, so are we whirled with the earth while thinking we stand still. It is more incredible that the moon, sun, Mars, Jupiter, Saturn, or the fixed stars should traverse their courses in twenty-four hours. It is absurd to imagine a primum mobile and give it a twenty-four-hour motion 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, then worse than insane is the motion of the primum mobile, in harmony with no other motion.
Ptolemy and the Peripatetics think all nature would be thrown into confusion by earth’s rapid rotation. Gilbert cites the earth’s diameter as 1718 German miles; the new moon’s greatest elongation 65, least 55, semi-diameters of earth; the sun at greatest eccentricity distant 1142 semi-diameters; Mars, Jupiter, Saturn far more distant. The firmament’s distances are indeterminable. If the primum mobile‘s convexity be estimated, it must travel in one hour as much space as three thousand great circles of earth; on the firmament’s convexity, more than eighteen hundred. No iron structure could withstand such velocity. The Chaldees believed the heavens light; but in light there is no such firmness, nor in Plotinus’s fire-firmament.
The Earth’s Soul and the Cause of Its Rotation
These final chapters conclude Gilbert’s magnetic philosophy of the Earth. Winds are only motions of exhalation along the Earth’s surface; the air current’s depth is trifling, and every region has various winds from different and opposite points.
Key Ideas
Verticity. Gilbert’s word for the polar turning power inherent in magnetic bodies — not a gyrating motion but an innate directing vigor, a virtus convertens. It is the property that makes a magnetized needle seek north and south, and it can be weakened, destroyed by fire, or restored by contact with a loadstone.
The terrella. A spherical loadstone shaped to model the earth. On its surface Gilbert traces poles, an equinoctial circle, meridians, parallels, and a magnetic horizon, and he shows that iron behaves on the little sphere exactly as compass needles behave on the great one. The terrella is the laboratory earth.
Coition rather than attraction. Gilbert rejects the word “attraction” for magnetic movements because it implies one body dragging another by force. Magnetic bodies come together, he argues, by mutual and harmonious approach — a coition in which both parties act, and which is always vigorous even when heavy matter resists.
The armed loadstone. A loadstone fitted with an iron cap or helmet at its pole. Gilbert devotes many chapters to testing whether the cap increases the stone’s native power or merely concentrates it, and he concludes that the armed stone lifts greater weights because the iron itself becomes a magnetic auxiliary, not because the stone’s virtue has grown.
Electric and magnetic bodies distinguished. Amber, jet, diamond, glass, sulphur, and sealing-wax attract light bodies by effluvia released through friction — an electric action. The loadstone works by a formal efficiency, a primary native strength. Electric attraction draws only the electric; magnetic bodies come together by joint forces, and the attracted iron is itself altered in the encounter.
The magnetic form. Gilbert calls it the form of the prime and principal globes — the radical, astral form proper to the earth, the sun, the moon, and the stars. A fragment of the moon would arrange itself lunatically; a fragment of the earth arranges itself terrestrially. This is not Aristotle’s prime form but a single formative power belonging to each globe.
The dip and variation as earthly evidence. The needle’s downward inclination, first discovered by Robert Norman in 1576, and its slow variation from true north, observed by Hariot, Hues, Wright, and Kendall on long voyages, are treated as measurable consequences of the earth’s magnetic constitution rather than as anomalies.
Themes
The book is, at bottom, an argument about how to know nature. Gilbert sets sure experiments against conjecture, and he repeatedly mocks the bookish philosophers who copy one another, cram the shops with volumes on occult causes, and never once test a claim. His contempt for the barber tossing Latin at the ignorant, for the alchemist veiling things in pedantic terminology, and for Cardan’s treasure-finding loadstone is the contempt of a man who has spent eighteen years handling stones.
Running beneath the method is a vision of the earth as a living, ordered body. Gilbert speaks of the earth’s bowels, its humors, its exhalations, its wombs where metals take shape. The loadstone is not a dead stone with a strange trick; it is the earth’s own matter, and its powers are the earth’s powers. When he says the foundations of the earth are magnetically conjoined and held together, he is answering Ptolemy’s fear that a rotating earth would fly apart — and he is also claiming that the planet coheres by love and good-will among its parts.
There is a polemical edge throughout. Gilbert honors Aristotle, Theophrastus, Ptolemy, Hippocrates, and Galen as sources from whom knowledge descended, but he insists that this age has discovered many things they would cheerfully adopt, and that their errors have been handed down from author to author while sciolists stray in perpetual darkness. The break with the schools is deliberate and complete.
Why It Matters
Edward Wright, in the address printed with the work, calls Gilbert his master and defends him against disparagers. John Dryden predicted that Gilbert would live till loadstones cease to draw. The book’s reputation rests on more than its conclusions. Gilbert first used the terms electric force, electric emanations, and electric attraction; he named the magnetic poles; he invented the versorium and two navigational instruments. He formed a loadstone into a terrella and made the earth itself an object of experiment.
The work also marks a turn in natural philosophy. Its insistence on repeated demonstration, its willingness to discard ancient authority, and its refusal to explain magnetic effects by sympathy, likeness, or imperceptible rods set a standard that later investigators inherited. The biographical tradition records that the manuscript of his other philosophical work was partly in English, and that no line of his handwriting survives with certainty — a fitting obscurity for a man whose real legacy was a method rather than a personality. What remains is the book itself: patient, combative, and convinced that the earth is a magnet, and that anyone with a needle, a stone, and steady hands can prove it.
