Georg Ohm: A Life in Five Chapters

Chapter 1 · A Locksmith Who Taught Himself Mathematics

Erlangen, and an education from a father

1789 – 1817 · Erlangen · Switzerland · Bamberg · Cologne

Georg Simon Ohm was born at Erlangen in Bavaria in March 1789. His father Johann Wolfgang Ohm was a *locksmith* — a skilled trade, not a profession — who had taught himself mathematics, philosophy and physics to a high standard, and who taught his sons.

The education was good enough that when Georg and his younger brother Martin were examined at the University of Erlangen, a professor reported that they had been given a training comparable to the best.

Martin became a professional mathematician of some standing.

Georg entered Erlangen in 1805, and left after three semesters, apparently having spent too much time on dancing, billiards and ice-skating. His father was furious and sent him to Switzerland to teach in a school.

He taught, studied on his own, returned, and completed his doctorate at Erlangen in 1811.

And then he could not get an academic position. He held a series of poorly paid school posts — Bamberg, and then from 1817 the Jesuit Gymnasium at Cologne.

The Cologne post is the important one, because the school had a *well-equipped physics laboratory* — unusually for a school — and Ohm had access to it.

He also had ambition. He was explicit in letters that he intended to do research good enough to earn a university chair, because a school post was a dead end and he wanted out.

The research he is remembered for was done in a school laboratory, by a schoolmaster, in his own time, as a means of escape.

“The galvanic circuit, treated mathematically.”

— Georg Simon Ohm, title of Die galvanische Kette, mathematisch bearbeitet (1827)

Why this matters

Ohm's law was worked out in a school physics laboratory by a schoolmaster doing research specifically to escape schoolteaching.

You have the locksmith's teaching and the school laboratory. What would you ask?

Ask Ohm

• “What could a locksmith teach you about mathematics?”
• “Why did you leave university after three semesters?”
• “What was it like being trapped in schoolteaching?”
• “How did a school come to have a physics laboratory?”
• “Did you always intend the work as an escape?”

Chapter 2 · A Source That Holds Steady

Why the voltaic pile made the measurement impossible

1825 – 1826 · Cologne

Ohm's first attempts used a *voltaic pile*, and they failed, and the reason is important.

A voltaic pile *drifts*. Its output falls as the reaction proceeds, as the brine dries, as the zinc corrodes and as bubbles of hydrogen accumulate on the plates — an effect called polarisation. Over the course of an afternoon's measurements the driving force is continuously changing, and there is no way to know by how much.

So if you measure the current for one wire, change the wire, and measure again, you cannot tell whether the difference is due to the wire or to the pile having weakened in the meantime.

Ohm's early published results, in 1825, were consequently wrong — he obtained a logarithmic relationship that does not hold.

The rescue came from *Thomas Johann Seebeck*, who had discovered in 1821 that a junction of two dissimilar metals held at different temperatures produces a small steady electromotive force. This is the *thermocouple*, and the thermoelectric effect.

Its virtue for Ohm is that it is *stable*. Keep one junction in boiling water and the other in melting ice, and it will produce the same driving force for hours, all day, indefinitely. It is small, but it does not drift.

With a steady source, Ohm could vary the conductor and be confident that any change in the current was due to the conductor alone.

His detector was a *torsion galvanometer* of his own construction: a magnetic needle suspended by a wire above the circuit, deflected by the current's magnetic effect — Ørsted's discovery of only five years earlier — with the deflection balanced by twisting the suspension, so the twist measured the current.

He then drew wires of the same metal to different *lengths* and different *thicknesses*, and measured.

Why this matters

The voltaic pile drifts continuously, so no comparative measurement is possible with it — Ohm's law had to wait for a source that held steady.

You have the drifting pile and the steady thermocouple. What is your question?

Ask Ohm

• “Why does a voltaic pile make the measurement impossible?”
• “What is a thermocouple, and why is it steady?”
• “Your first published result was wrong — what happened?”
• “How did you measure a current at all?”
• “How much does an experiment depend on the source?”

Chapter 3 · Length and Thickness

The relationship, 1827

1827 · Cologne · Berlin

Ohm's measurements gave a clean result.

For a wire of given material, the *current* is inversely proportional to the *length*: double the length, halve the current. And it is proportional to the *cross-sectional area*: double the thickness in area, double the current.

So each conductor has a property — a *resistance* — proportional to length and inversely proportional to area, and depending on the material.

And the current in the circuit is the driving force divided by the total resistance of the whole circuit, including the source itself.

That last qualification matters and is often left out. Ohm was clear that the *internal* resistance of the source is part of the total, which is why connecting a low-resistance wire does not give an unlimited current.

He published *Die galvanische Kette, mathematisch bearbeitet* — The Galvanic Circuit, Treated Mathematically — in Berlin in 1827.

The *form* of the book is what caused the trouble. Ohm did not simply present the measurements. He built a mathematical theory, taking as his model *Fourier's* treatment of heat conduction: just as heat flows down a temperature gradient at a rate depending on conductivity, electricity flows down a gradient of what he called electroscopic force at a rate depending on the conductor.

That analogy is deep and correct, and it was ahead of what German physics was prepared to accept.

He also had no idea what a current *is*. The electron was discovered seventy years later. Ohm had a quantity that flows, a driving force, and a resistance — three quantities and a relationship between them, with no account of the underlying physical reality at all.

And the relationship holds, for metallic conductors at constant temperature, with remarkable accuracy.

Why this matters

Ohm modelled electricity on Fourier's theory of heat flow, which is a deep and correct analogy that German physics was not ready to accept.

You have the wires and the relationship. What would you ask him?

Ask Ohm

• “How does resistance depend on a wire's shape?”
• “Why does the source's own resistance matter?”
• “Why model electricity on the flow of heat?”
• “What did you think was flowing?”
• “Where does your law stop holding?”

Chapter 4 · A Web of Naked Fancies

The reception, and a resignation

1827 – 1833 · Berlin · Cologne

The reception in Germany was hostile, and the reasons are worth understanding because they are not simply stupidity.

German physics at the time was substantially influenced by *Naturphilosophie*, which regarded nature as an organic unity to be grasped philosophically. Reducing an electrical phenomenon to an equation looked, to that school, like a category error — taking something living and treating it as a machine.

*Georg Friedrich Pohl*, a Berlin physicist, reviewed the book and called it, in effect, a *web of naked fancies* whose only object was to detract from the dignity of nature.

The Prussian *Minister of Education* is reported to have said that a physicist who professed such heresies was unworthy to teach science.

Ohm had published the book expecting it to earn him a university chair. Instead it damaged him. He *resigned* his post at Cologne in 1828 — whether pushed or in disgust is not entirely clear — and spent about six years in Berlin without a proper position, doing some teaching at a military school and living on very little.

He was bitter about it, and said so in letters.

There were other factors. Ohm was outside the Berlin establishment, was a schoolmaster rather than a professor, and had published a wrong result two years earlier which had damaged his credibility. And the book is genuinely difficult, opening with a substantial mathematical preamble that many readers could not follow and that obscures the experimental results buried inside it.

Meanwhile the law was being independently rediscovered and confirmed elsewhere, notably by *Claude Pouillet* in France and *Charles Wheatstone* in England, whose measurements were widely accepted.

Why this matters

German physics rejected Ohm partly because reducing a natural phenomenon to an equation looked like a category error to the Naturphilosophie tradition.

You have the review, the resignation and the six years. What is your question?

Ask Ohm

• “What did Pohl's review actually say?”
• “Why did a mathematical treatment offend people?”
• “How much did your earlier wrong paper cost you?”
• “Was the book harder to read than it needed to be?”
• “How did you live for six years without a post?”

Chapter 5 · London Honours What Berlin Dismissed

The Copley Medal, and a chair at sixty-three

1833 – 1854 and after · Nuremberg · London · Munich

In 1833 Ohm obtained a position at the *polytechnic school at Nuremberg* — a technical institution, not a university — and eventually became its director. It was a step up and it was not what he wanted.

Recognition came from abroad.

In 1841 the *Royal Society of London* awarded him the *Copley Medal*, its highest honour, for work its own country had dismissed fourteen years earlier. The following year he was elected a foreign member.

The reason British physicists valued it is straightforward: they were building *telegraphs*. A telegraph line is a very long conductor, and whether a signal will get to the other end depends entirely on the relationship between driving force, resistance and current. Wheatstone in particular needed exactly this law, and it worked.

So the theoretical result Berlin found offensive was, in Britain, the thing that made an industry possible.

German recognition followed the foreign honour, as it usually does. He was elected to the Bavarian Academy, and in 1849 finally obtained a university position at *Munich* — as an extraordinary professor, at sixty.

He was made a *full professor* in 1852, at *sixty-three*. He held the chair for two years.

He died at Munich on 6 July 1854, aged sixty-five.

In 1881, at the International Congress of Electricians in Paris, the unit of *resistance* was named the *ohm*.

He also did substantial work on *acoustics*, proposing what is called Ohm's acoustic law: that the ear analyses a complex sound into its constituent simple tones, so that the perceived quality of a note depends on which harmonics are present. Helmholtz developed it into the modern theory of hearing.

His career is the standing example of first-rate work rejected because of *how it was expressed* and *who expressed it*.

Why this matters

British physicists valued Ohm's law because they were building telegraphs and needed exactly that relationship — the same result Berlin had called a fancy.

You have the Copley Medal and the chair at sixty-three. What would you ask?

Ask Ohm

• “Why did the British need your law so badly?”
• “What did the Copley Medal mean to you?”
• “Did Germany ever apologise?”
• “What is your acoustic law about?”
• “Would you publish it differently?”

What Ohm changed

The relationship Ohm established is the first thing anybody learns about a circuit, and the unit of resistance carries his name. It made the electric telegraph calculable and the electrical industry possible. His career is also the standing example of first-rate work rejected because of how it was expressed and who expressed it — a schoolmaster using mathematics in a tradition that distrusted both.

A debate that continues

Ohm's 1825 paper contained a wrong logarithmic relationship caused by his drifting voltaic pile, which damaged his credibility before the correct 1827 work appeared; and the law was independently confirmed by Pouillet and Wheatstone, whose versions were more readily accepted.

Keep exploring — ask Ohm

• “What would a better galvanometer have let you measure?”
• “How should a discipline judge work from outside it?”
• “What is actually flowing in a wire?”

Related lives

• Gustav Kirchhoff — Who Read The Sun's Chemistry
• Alessandro Volta — Who Built A Battery Without A Frog
• Hans Christian Ørsted — Whose Compass Needle Turned Sideways
• Hermann von Helmholtz — Who Measured the Unmeasurable

Related themes

Current, voltage and resistance · Circuits · Conductors