William Gilbert

Chapter 1 · Physician to the Queen

A respectable career, and seventeen years of private experiment

1544 – 1600 · Colchester · Cambridge · London

William Gilbert was born at Colchester in May 1544, the son of the town's recorder. He went to St John's College, Cambridge, took his medical degree there in 1569, and set up in London.

He was extremely successful. He became a Fellow and then President of the College of Physicians, and in 1601 was appointed physician to Queen Elizabeth I — and, after her death, to James I. He never married, lived in Wingfield House in St Peter's Hill, and had money.

And for about seventeen years, at his own expense and alongside a full medical practice, he investigated the loadstone.

The literature on magnets in 1580 was voluminous and mostly rubbish. It had accumulated for centuries by copying, and it held that garlic destroys a magnet's power; that a diamond will steal a loadstone's virtue; that a magnet placed under a sleeping wife's pillow will make her confess her adultery; that magnets heal wounds and reconcile spouses; that there is an island of loadstone in the north which draws ships' nails out of their hulls.

Gilbert's method was to try them.

He rubbed magnets with garlic and they worked as before. He put diamonds beside loadstones and nothing happened. He tested the medical claims and found nothing. He worked through the received literature systematically and found it, in his own judgement, worthless — and he said so, with some contempt, in print.

That is unusual for 1600. It is one of the earliest sustained demonstrations that a written tradition can be simply *wrong*, and that an afternoon's testing settles what a thousand years of copying cannot.

“The Earth itself is a great magnet.”

— William Gilbert, De Magnete (1600)

Why this matters

Gilbert tested a centuries-old written tradition item by item and found nearly all of it false — one of the earliest demonstrations that authority can simply be checked.

You have the garlic, the diamond and the seventeen years. What would you ask?

Ask Gilbert

• “What did the books claim a loadstone could do?”
• “Does garlic really destroy a magnet?”
• “Why spend seventeen years and your own money on this?”
• “How did a busy physician find the time?”
• “Was it dangerous to call the ancients wrong?”

Chapter 2 · The Little Earth

A loadstone ground into a sphere

1580s – 1600 · London

The compass was the most important instrument in the world in 1600, and nobody knew why it worked.

The standing explanations were that the needle is drawn toward the *pole star*, or toward a great mountain or island of loadstone somewhere in the north.

There was also a puzzle. Robert Norman, a compass-maker in Wapping, had published in 1581 that a needle carefully balanced *before* magnetising will *dip downward* at one end after it is magnetised, and that the angle of dip varies with location. That is not what a horizontal attraction toward a distant point would do.

Gilbert's move is one of the great experimental ideas.

He took a loadstone and had it ground into a perfect *sphere*, which he called a *terrella* — a little Earth. Then he took a very small pivoted needle and walked it over the surface.

The needle *points along the surface*, exactly as a compass points on the Earth. Move it toward the sphere's pole and the needle *dips downward*, increasing as it approaches, exactly as Norman's needle does at higher latitudes. At the equator of the sphere the needle lies flat. At the pole it stands vertical.

Every behaviour of the compass over the whole Earth is reproduced, in miniature, on a ball of magnetised stone.

The conclusion follows and it is enormous: the needle is not drawn by a star or an island. It is drawn by *the globe under our feet*, and that globe is itself a magnet.

A model that reproduces the phenomena is not proof — but a model that reproduces *all* of them, including the awkward one nobody could explain, is a very powerful argument.

Why this matters

The terrella reproduces every behaviour of the compass in miniature, including the dip nobody could explain, which is why the Earth-as-magnet conclusion was compelling.

You have the sphere of stone and the needle walking over it. What is your question?

Ask Gilbert

• “Why grind the loadstone into a sphere?”
• “What does the needle do as it nears the pole?”
• “Why can't the pole star be pulling the needle?”
• “Is a model that behaves the same a proof?”
• “What did Robert Norman find that puzzled everyone?”

Chapter 3 · Coining the Word Electric

And insisting the two effects have nothing to do with each other

1600 · London

It had been known since antiquity that *amber*, rubbed, will attract small light bodies — chaff, straw, dust. The Greek for amber is *elektron*.

And it had long been assumed that this is the same power as a loadstone's, or a weaker version of it.

Gilbert separated them, decisively.

First he showed the effect is not peculiar to amber. He tested a long list of substances and found that many of them — jet, sulphur, sealing wax, glass, resin, several gemstones — attract light bodies when rubbed. He called these *electrics*, and the ones that do not, such as the metals, *non-electrics*.

So the word *electric* is Gilbert's, coined in *De Magnete* in 1600, and it is now attached to a vast section of physics and to the entire industrial world.

He built an instrument to detect it: the *versorium*, a light metal needle pivoted freely on a point, which swings toward a rubbed body. It is the first electroscope.

Then he listed the differences. The magnetic virtue acts only on iron; the electric attracts almost anything light. Magnetism passes through interposed bodies; the electric effect is blocked by paper or flame or moisture. A magnet's power is permanent; the electric effect requires rubbing and fades. A magnet both attracts and *repels* and has poles; the electric attraction has no poles and, so far as he could see, no repulsion. Heat destroys magnetism; heat and moisture destroy the electric effect for different reasons.

His conclusion: they are *entirely different powers*, with no connection whatever.

That is exactly wrong, and it is wrong for good reasons. The connection Ørsted found in 1820 requires a *moving* charge, and Gilbert had no way of producing a steady current. The evidence available to him genuinely pointed the other way.

Why this matters

Gilbert's insistence that electricity and magnetism are unrelated was wrong and well-reasoned: the connection requires moving charge, which nobody could produce for two hundred years.

You have the word and the separation. What would you ask him?

Ask Gilbert

• “Why call the amber effect 'electric'?”
• “How does the versorium detect the effect?”
• “What differences convinced you the two powers were separate?”
• “What evidence would have linked the two for you?”
• “Why does rubbing amber work and rubbing iron not?”

Chapter 4 · De Magnete

1600, and one of the first books of experimental science

1600 · London

*De Magnete, Magneticisque Corporibus, et de Magno Magnete Tellure* — On the Magnet, Magnetic Bodies, and the Great Magnet the Earth — was published in London in 1600.

It is one of the founding books of experimental science, and it is *organised around experiments*. The results are described in enough detail to be repeated. Gilbert marks the ones he considers particularly important with a special symbol in the margin, so a reader can find them. He states which claims he has tested himself and which he has only read.

His address to the reader is worth knowing: he says he is writing for those who look for knowledge not only in books but in things themselves, and he expects to be attacked for it.

Beyond the terrella, the book establishes a great deal. Iron can be *magnetised* by stroking with a loadstone, and also by *hammering* it while it lies aligned north–south — which is why iron tools and church weathervanes become magnetic over time. Heating a magnet to red heat *destroys* its magnetism. Magnetic attraction passes through interposed bodies. A loadstone broken in two gives two complete magnets, each with two poles, rather than a separated north and south.

That last is a genuinely important observation: you cannot isolate a single magnetic pole. It is still true, and it is one of the deep differences between magnetism and electricity.

He also argued for the *rotation of the Earth*, on magnetic grounds — an early and open Copernican position for an Englishman in 1600 — and held that magnetism is what makes the Earth turn.

And he held that the Earth possesses a *magnetic soul*. That is not a slip; it is argued at length. He thought the magnetic virtue was an animate power, and that the loadstone is in some sense alive.

Why this matters

De Magnete describes its experiments in enough detail to be repeated and marks which claims the author tested himself — a standard for scientific writing in 1600.

You have the book, the marginal symbols and the magnetic soul. What is your question?

Ask Gilbert

• “Why mark the important experiments in the margin?”
• “What happens when you break a magnet in half?”
• “Why do church weathervanes become magnetic?”
• “What do you mean by a magnetic soul?”
• “Why did you argue the Earth turns?”

Chapter 5 · What Came of It

Kepler, Galileo, Bacon's objection, and plague

1600 – 1603 and after · London

*De Magnete* was read immediately and widely.

Galileo praised it, and said he envied Gilbert. He also complained that Gilbert was a poor mathematician, which is fair.

*Kepler* took it much further, and it is the most consequential reception. Gilbert had proposed that a magnetic force reaches out from a body and acts on another at a distance. Kepler took that seriously as a *model for the force holding the planets in their orbits* — a force emanating from the Sun and sweeping the planets round. That is wrong in detail and it is the first serious attempt to explain planetary motion by a physical force rather than by geometry or by divine machinery, and it leads, by way of Newton, to gravitation.

*Francis Bacon* objected, and his objection is worth knowing because it is the standard criticism. Bacon complained that Gilbert had made a whole philosophy out of a single set of experiments — that having found one thing out about magnets, he explained everything by magnetism, including the Earth's rotation and the movement of the heavens.

That is a real fault, and it recurs throughout the history of science: a genuine discovery turned into a universal principle it cannot support.

Gilbert died in London in November or December 1603, aged fifty-nine, a few months after Queen Elizabeth. He probably died of plague, which was severe in London that year.

He left his books, instruments, minerals and his terrella to the College of Physicians. They were destroyed in the Great Fire of London in 1666.

So the little Earth that made the argument does not survive. The book does.

Why this matters

Kepler took Gilbert's magnetic force acting at a distance as his model for what holds planets in orbit — the first physical explanation of planetary motion.

You have Kepler's use of it and Bacon's objection. What would you ask?

Ask Gilbert

• “What did Kepler do with your magnetic force?”
• “Is Bacon right that you explained too much by magnetism?”
• “How did Galileo receive the book?”
• “What was lost when the College burned?”
• “How do you stop a real discovery becoming a universal theory?”

What Gilbert changed

De Magnete is one of the founding books of experimental science, and the discovery that the Earth is a magnet explained navigation's central instrument for the first time. The word electric is Gilbert's. Kepler took his magnetic force acting at a distance as the model for what holds planets in their orbits, which leads by way of Newton to gravitation.

A debate that continues

Gilbert insisted that electricity and magnetism are entirely separate powers — the opposite of the truth, though the evidence available to him pointed that way — and Francis Bacon's charge that he built a whole philosophy out of one set of experiments is a fair criticism.

Keep exploring — ask Gilbert

• “Which of the old claims about loadstones came closest to being true?”
• “What would you have done with a battery?”
• “How much of your book would survive testing now?”

Related lives

• Johannes Kepler — Discoverer of Planetary Motion
• Galileo Galilei — Father of Modern Science
• Michael Faraday — Discoverer of Electromagnetic Induction
• Hans Christian Ørsted — Whose Compass Needle Turned Sideways

Related themes

Magnets and magnetic fields · The Earth's magnetic field · Experimental method