Hans Christian Ørsted

Chapter 1 · A Town With No School

Rudkøbing, and an education assembled from neighbours

1777 – 1801 · Rudkøbing · Copenhagen

Hans Christian Ørsted was born in August 1777 above his father's apothecary shop in Rudkøbing, a small town on the island of Langeland. The town had no school worth attending.

So he and his younger brother Anders were educated by whoever would teach them. A German wigmaker and his wife taught them German and reading. The town surveyor taught arithmetic. The pastor taught Latin and Greek. The mayor taught English and French. They worked in the shop and learned chemistry from the preparations.

At twelve he was working in the apothecary's laboratory. At seventeen he and his brother walked into Copenhagen and took the university entrance examination. Both passed with distinction. Anders became a lawyer and eventually *Prime Minister of Denmark*.

Ørsted took a degree in pharmacy and then a doctorate in philosophy in 1799, on Kant.

And this is the fact that shapes everything. In 1801 to 1803 he travelled in Germany and France on a scholarship, and in Germany he encountered *Naturphilosophie* — the Romantic philosophy of nature associated with Schelling and, in physics, with Johann Wilhelm Ritter, whom Ørsted met and admired.

Its central conviction: the apparently separate forces of nature — electricity, magnetism, heat, light, chemical affinity — are *manifestations of one underlying unity*. They must be connected, because nature is a single thing.

Most experimental physicists dismissed this as mystical, and much of it was. And it kept Ørsted looking for a connection between electricity and magnetism for the better part of twenty years, when the settled scientific view — Gilbert's view, still authoritative — was that no such connection exists.

“The magnetic effect of the electric current has a circular motion round it.”

— Hans Christian Ørsted, Experimenta circa effectum conflictus electrici in acum magneticam (July 1820)

Why this matters

A Romantic philosophy most physicists dismissed as mystical is what kept Ørsted looking for a link between electricity and magnetism for two decades.

You have the town with no school and the philosophy from Germany. What would you ask?

Ask Ørsted

• “How do you get educated in a town with no school?”
• “What did Naturphilosophie actually claim?”
• “Why did other physicists dismiss it?”
• “Can a wrong philosophy lead to a right discovery?”
• “What did the apothecary's shop teach you?”

Chapter 2 · The Needle Moves

A lecture in April 1820

1820 · Copenhagen

Ørsted became professor at Copenhagen in 1806 and looked, on and off, for a link between electricity and magnetism for fourteen years.

He had reasons for thinking it might involve heat or light rather than a direct effect, and he had tried a number of arrangements without result. He seems to have expected any effect to be along the wire, not across it, which is why earlier attempts failed.

In April 1820, during a lecture demonstration to advanced students, he had a voltaic pile, a wire and a compass needle on the bench. He closed the circuit.

The needle moved.

The movement was small. Accounts differ on the details and on whether it was entirely unplanned — Ørsted's own later statement suggests he had been intending to try the arrangement and that the moment arrived during the lecture.

He did not announce it.

He spent the next *three months* attacking the result. He built stronger piles, to get a larger effect. He used thicker wires and better connections. He tried different metals. He used larger and more sensitive needles. He checked for every alternative cause he could think of: heating of the wire, air currents, mechanical vibration, the magnetism of the apparatus itself.

And he did the crucial thing: he moved the wire *above* the needle and then *below* it.

That is the experiment that produced the real discovery. Not that a current affects a magnet — that something happens near the wire — but *what kind* of effect it is.

Why this matters

Ørsted saw the effect in April and did not publish until July, spending three months trying to destroy his own result — which is what turned an anecdote into a discovery.

You have the twitch and the three months of doubt. What is your question?

Ask Ørsted

• “What did you actually see during the lecture?”
• “Why not publish immediately?”
• “What alternative causes did you have to rule out?”
• “Why had fourteen years of looking failed before?”
• “How much of it was luck?”

Chapter 3 · At Right Angles

A force unlike any other force known

1820 · Copenhagen

Here is what the needle actually does, and it is very strange.

It does not point *toward* the wire. It does not point *away from* it. Those are what you would expect: every force known in 1820 — gravity, electrostatic attraction, magnetic attraction between poles — acts along the *line joining* the two bodies. Attraction or repulsion, along the line. That is what a force does.

The needle sets itself at *right angles* to the wire.

And if you move the wire from above the needle to below it, the needle *reverses*.

Put those together and the picture is unavoidable: the magnetic effect *circles the wire*. The wire is surrounded by a *circular* magnetic influence, like rings of a ripple around a dropped stone, and the needle simply aligns itself with the ring it happens to be sitting in. Above the wire the ring runs one way; below it, the other.

Ørsted stated it plainly: the magnetic effect of the electric current has a circular motion round it.

That is why the discovery mattered so much and why it was so difficult. It is not merely a new instance of a known kind of force. It is a force of a kind nobody had ever described — one that does not act along the line between two objects, but *around* something.

It is also the reason the effect had been missed for so long. If you are looking for an attraction or a repulsion — bringing a magnet near a wire and watching for it to be pulled — you will find nothing, because that is not what happens.

He had to look for the wrong kind of thing to find it.

Why this matters

Every force known in 1820 acted along the line joining two bodies; the magnetic effect of a current acts around the wire, which is why it had been missed.

You have the circular force and the reversing needle. What would you ask?

Ask Ørsted

• “Why is a circular force so strange?”
• “What happens when you move the wire under the needle?”
• “Why did looking for attraction guarantee failure?”
• “How would you describe the shape of the effect?”
• “Did you have any account of why it should be circular?”

Chapter 4 · Four Pages of Latin

July 1820, and Europe in six weeks

1820 – 1821 · Copenhagen · Paris · London · Geneva

On 21 July 1820 Ørsted published a four-page pamphlet in *Latin*: *Experimenta circa effectum conflictus electrici in acum magneticam* — Experiments on the effect of a current of electricity on the magnetic needle.

He chose Latin deliberately, as the language every European scientist could read, and he did not send it to a journal. He *printed it himself and posted it* to the leading scientific figures across Europe.

The effect was extraordinary.

In Geneva, at a demonstration by Auguste de la Rive, *François Arago* saw it and carried the news to Paris. On 4 September 1820 he reported it to the Académie des Sciences.

*André-Marie Ampère* heard the report. Within a *week* he had repeated the experiment. Within *two weeks* he had discovered that two parallel current-carrying wires attract or repel *each other*, depending on the direction of the currents — which is a new phenomenon, not just a new instance. Within a few months he had a mathematical theory of the forces between currents and had proposed that magnetism itself is caused by circulating currents at the molecular level.

That is one of the fastest pieces of theoretical development in the history of physics.

In London, *Michael Faraday* read the pamphlet, repeated it, and in 1821 produced *electromagnetic rotation* — arranging a wire so that the circular force made it revolve continuously around a magnet. That is the principle of the electric motor.

And in 1831 Faraday completed the argument in the other direction: if a current produces magnetism, then a *changing* magnetic field should produce a current. That is *electromagnetic induction*, and it is the generator, the transformer and the whole electrical supply industry.

Ørsted never found induction himself.

Why this matters

Ørsted printed four pages of Latin and posted them across Europe, and within six weeks Ampère had a mathematical theory of forces between currents.

You have the pamphlet and what happened in six weeks. What is your question?

Ask Ørsted

• “Why print it yourself and post it rather than submit it?”
• “What did Ampère do within two weeks?”
• “How did Faraday get a motor out of your result?”
• “Why did you not find induction yourself?”
• “What was it like being overtaken in a fortnight?”

Chapter 5 · Aluminium, and Science for Everybody

A first metal, a friendship, and a society that still exists

1825 – 1851 · Copenhagen

Ørsted's other work is substantial and much less known.

In 1825 he was the first to isolate *aluminium*, by reducing aluminium chloride with potassium amalgam. He obtained a small quantity of the metal and described it as resembling tin in colour and lustre. His preparation was impure and he did not pursue it; Friedrich Wöhler improved the method in 1827, and for a long period Wöhler was given sole credit. Modern assessment restores Ørsted's priority for the first preparation.

He worked on the *compressibility of liquids*, showing that water is very slightly compressible — which had been disputed — and built a piezometer to measure it.

In 1824 he founded the *Selskabet for Naturlærens Udbredelse*, the Society for the Dissemination of Natural Science, to bring science to the general public through lectures and publications. It still exists and still awards the Ørsted Medal.

He cared about this a great deal. His view was that science belongs to the public and should be taught to them, and he wrote and lectured for general audiences constantly. He also wrote poetry, and a philosophical work, *The Soul in Nature*.

He was a close friend of *Hans Christian Andersen*, who was much younger, and encouraged him early. Andersen said Ørsted had told him, when the fairy tales were dismissed as trifles, that the novels would make him famous and the tales would make him immortal.

Ørsted was rector of the University of Copenhagen and a national figure. He died in Copenhagen in March 1851, aged seventy-three. Something like two hundred thousand people are said to have attended the funeral procession.

The unit of magnetic field strength in the older CGS system is the *oersted*.

Why this matters

Ørsted founded a society for teaching science to the public that still exists, on the conviction that science belongs to everybody.

You have the aluminium, the society and Andersen. What would you ask him?

Ask Ørsted

• “How did you make aluminium in 1825?”
• “Why does the public need to be taught science?”
• “What did you say to Hans Christian Andersen?”
• “Is water really compressible?”
• “Was the philosophy worth the ridicule?”

What Ørsted changed

Everything electromagnetic descends from those four pages: the electromagnet, the motor, the generator, the transformer and the whole of the electrical industry. Ampère built a mathematical theory of currents within weeks, and Faraday reversed the argument in 1831 to produce induction. Ørsted also isolated aluminium for the first time and founded a society for public science that still exists.

A debate that continues

The discovery is routinely told as a lucky accident, which erases fourteen years of deliberate searching and three months of attempting to disprove the result; and Ørsted's priority for the first isolation of aluminium was long credited to Wöhler instead.

Keep exploring — ask Ørsted

• “How long should you attack your own result before publishing?”
• “What made you keep looking for fourteen years?”
• “Which of your other results should be better known?”

Related lives

• Michael Faraday — Discoverer of Electromagnetic Induction
• Alessandro Volta — Who Built A Battery Without A Frog
• William Gilbert — Who Made A Little Earth Of Stone
• James Clerk Maxwell — Who Bound Light to Electromagnetism

Related themes

Electromagnetism · Magnetic fields around currents · The electric motor