Robert Brown

Chapter 1 · Four Thousand Species

Naturalist on a survey of the Australian coast

1773 – 1810 · Montrose · Edinburgh · Australia · London

Robert Brown was born at Montrose in Scotland in December 1773, the son of an episcopalian clergyman. He studied medicine at Edinburgh, did not complete the degree, and joined a Scottish regiment as an ensign and assistant surgeon, serving in Ireland — where, having very little to do, he botanised obsessively and taught himself German so he could read the continental literature.

In 1798 he met Sir Joseph Banks in London. Banks had sailed with Cook, effectively ran British botany, and had the best private herbarium and library in the world. He recruited Brown as naturalist aboard HMS *Investigator*, under Matthew Flinders, for the survey that would circumnavigate and chart the coasts of Australia.

The voyage ran from 1801 to 1805 and was difficult: the ship rotted, Flinders was later imprisoned by the French at Mauritius for six years, and a shipwreck lost part of the collections.

Brown came back with around four thousand species, the great majority of them new to science, and spent five years working through them. *Prodromus Florae Novae Hollandiae* (1810) is the foundation of Australian botany. He also began to reorganise plant classification along natural lines rather than Linnaeus's artificial sexual system, and he established the distinction between gymnosperms and angiosperms — whether the ovule sits naked or enclosed.

He became Banks's librarian, and on Banks's death inherited the use of the collections for life.

Why this matters

Brown's Australian collections and his shift toward natural classification made him, by the 1820s, the most respected descriptive botanist alive.

You have the voyage and the four thousand species. What would you ask him?

Ask Brown

• “What was collecting on the Australian coast actually like?”
• “Why abandon Linnaeus's system for a natural one?”
• “What is the difference between a naked and an enclosed ovule?”
• “What did Banks's patronage make possible?”
• “How do you work through four thousand new species?”

Chapter 2 · A Constant Body in Every Cell

Naming the nucleus, 1831

1831 · London

In 1831, examining orchids under the microscope, Brown noticed something that others had glimpsed and nobody had made anything of. Inside the cells of the epidermis of the leaves — and then, when he looked, in cell after cell across many species — there was a single opaque rounded body.

What mattered was not seeing it. It was recognising that it is *constant*: not an occasional inclusion or a granule of stored material, but a regular, expected component of the cell, present as a rule rather than an exception.

He called it the *nucleus* — Latin for a kernel, the small hard thing at the centre.

He reported it almost in passing, in a paper on orchid fertilisation, and made no large claims for it. He did not know what it did. He suspected it had something to do with the development of the cell, and said no more than that.

Six years later Schleiden, and then Schwann, built cell theory partly on the presence of that body: it was the nucleus, present in plant and animal cells alike, that let Schwann recognise the same structure in a tadpole's notochord that Schleiden had described in plants. The nucleus was the common feature that made the two kingdoms comparable.

Its function — that it holds the chromosomes and therefore the inherited material — was not established for another sixty or seventy years.

Why this matters

The nucleus was the structure common to plant and animal cells that made cell theory possible, and Brown's contribution was recognising it as a constant rather than an oddity.

You have the small body present in every cell. What is your question?

Ask Brown

• “How did you know the nucleus was a constant feature?”
• “What did you think it was for?”
• “Why report it almost in passing?”
• “Why does naming a thing matter so much?”
• “What made cell theory possible that had not been before?”

Chapter 3 · The Pollen That Would Not Keep Still

June 1827

1827 · London · Soho Square

In June 1827 Brown was examining the pollen of *Clarkia pulchella*, a North American plant, suspended in water under a simple single-lens microscope made for him by the instrument-maker Bancks.

Inside the pollen grains were small particles, and they would not keep still. The motion was irregular, in every direction, never stopping, with no drift and no pattern — a ceaseless jostling.

The obvious explanation was that he was watching something alive. Pollen is a reproductive structure; the particles might be tiny organisms or animate corpuscles, and there was a serious contemporary theory, going back to Buffon, of *organic molecules* — living units common to all organisms.

Brown tested it, and the sequence of tests is a model of how to destroy your own best hypothesis.

First he used pollen from herbarium specimens that had been dead and dried for decades, and in some cases over a century. The particles moved exactly as before. Whatever it was, it was not the activity of a living thing.

He could have stopped there. He did not. He left the living world entirely and ground up inanimate substances fine enough to suspend in water: powdered glass, soot, metals, minerals, rock — and, famously, a fragment chipped from a stone of the Great Sphinx at Giza.

Every one of them showed the same restless motion. It had nothing to do with life at all.

“The motion was observed in particles of every substance I examined, organic or not.”

— Robert Brown, A Brief Account of Microscopical Observations… (1828)

Why this matters

Brown tested his own most attractive hypothesis to destruction using century-old dead pollen and a chip of the Sphinx — a model of self-directed falsification.

You have the jostling particles and everything they were not. What would you ask?

Ask Brown

• “Why use pollen that had been dead a hundred years?”
• “Why go as far as grinding up a piece of the Sphinx?”
• “How do you test an explanation you would like to be true?”
• “What did the motion actually look like?”
• “Were you disappointed it was not alive?”

Chapter 4 · And No Cause

A pamphlet that stops where the evidence stops

1828 – 1829 · London

Brown published in 1828 as a short pamphlet, privately printed and circulated to colleagues: *A Brief Account of Microscopical Observations made in the months of June, July and August 1827, on the Particles contained in the Pollen of Plants; and on the general Existence of active Molecules in Organic and Inorganic Bodies*.

The title is longer than most of the argument. The pamphlet reports what he saw, reports what he did to eliminate a vital cause, and states the general result: the motion occurs in particles of any substance whatever, provided they are small enough and suspended in a fluid.

And then it stops. He offers no cause. He does not propose currents, or evaporation, or heat, or electricity, or attraction between particles — all of which were suggested by others, and all of which he had considered and could not support.

He was also careful to say he was not the first to see such motion; others had noticed it, and he lists them.

This restraint is the thing worth learning from. Having demolished the natural explanation, he had every incentive and every opportunity to supply a replacement, and a plausible guess would have cost him nothing at the time. He declined, on the stated principle that a conclusion which has run ahead of a trial is worse than no conclusion.

The result is that the phenomenon carries his name for an observation and a set of eliminations, not for a theory — which is, on reflection, an unusually honest reason to have something named after you.

Why this matters

Brown published a phenomenon with no explanation attached because he had none, which is why the observation survived intact for the person who could explain it.

You have the pamphlet with the missing final section. What is your question?

Ask Brown

• “Why not offer a cause when everyone expected one?”
• “Which explanations did you consider and reject?”
• “Is a result without a theory worth publishing?”
• “Why point out that others had seen it before you?”
• “Did people press you to guess?”

Chapter 5 · Eighty Years Later

The motion becomes the proof that atoms are real

1858 – 1908 · London · Bern · Paris

Brown never learned the cause. He continued as the leading botanist in Britain, was elected President of the Linnean Society, advised Darwin before the *Beagle* voyage — Darwin thought him the finest observer alive, and also found him maddeningly cautious about publishing — and died in London in June 1858, aged eighty-four.

He died three weeks before the Darwin–Wallace papers were read to the Linnean Society, in the rooms where he had presided.

The explanation came in 1905, in one of Albert Einstein's four papers of that year. A suspended particle is being struck constantly, from every side, by the moving molecules of the surrounding fluid. Most of the time the blows roughly cancel. But they are random, so at any instant slightly more arrive from one side than another, and the particle is knocked. Being small, it is knocked visibly.

Einstein did the statistics and derived a testable prediction: how far, on average, a particle of a given size should wander in a given time, at a given temperature.

Jean Perrin measured it, painstakingly, and reported in 1908 that the numbers matched. From them he extracted a value for Avogadro's number.

That settled a question that was still genuinely open: whether atoms and molecules are real physical objects or merely a convenient bookkeeping device. Serious physicists — Ostwald, Mach — had held the second view. After Perrin, almost nobody did.

So a botanist's refusal to guess about some jiggling pollen became, eighty years later, one of the decisive proofs that matter is made of particles.

Why this matters

Brownian motion supplied the measurement that ended serious scientific doubt about whether atoms physically exist.

You have the observation and the proof it became. What would you ask him?

Ask Brown

• “What would you have said to Einstein?”
• “How does random bombardment produce visible movement?”
• “Why did anyone still doubt that atoms exist in 1900?”
• “Darwin found you too cautious about publishing — was he right?”
• “Does it matter that your name is on a motion you could not explain?”

What Brown changed

The motion Brown described became, eighty years later, one of the decisive proofs that matter is made of particles in constant motion — Einstein explained it in 1905 and Perrin's measurements in 1908 effectively ended scientific doubt about the reality of atoms. The nucleus he named in 1831 is in every biology textbook, and his refusal to supply a cause he did not have remains a model of how to report a result.

A debate that continues

Brown was not the first to observe the motion, as he was careful to say, and how much of the credit for identifying it as a general physical phenomenon belongs to him rather than to earlier observers is occasionally revisited.

Keep exploring — ask Brown

• “Which of your botanical results should be better known?”
• “When is it right to say you do not know?”
• “What should Darwin have asked you before he sailed?”

Related lives

• Albert Einstein — Nobel Laureate · Author of Relativity
• Carl Linnaeus — Who Gave Every Living Thing Its Name
• Charles Darwin — Author of On the Origin of Species
• Theodor Schwann — Who Said Animals Are Built Like Plants

Related themes

Diffusion and particle motion · Cells and the nucleus · Evidence for particles