Robert Boyle

Chapter 1 · The Fourteenth Child of the Richest Man in Ireland

Money, and what it bought

1627 – 1655 · Lismore Castle · Eton · Geneva · Florence · Stalbridge

Robert Boyle was born at Lismore Castle in County Waterford in January 1627, the fourteenth child and seventh son of Richard Boyle, the first Earl of Cork — a Kentish adventurer who had arrived in Ireland with almost nothing and become the wealthiest man in the country by means that were, at best, sharp.

Boyle was sent to Eton at eight, and at eleven set off on a grand tour with a tutor. In Geneva in 1640, during a violent thunderstorm at night, he had a religious experience that determined the rest of his life: a conviction of the reality of God and of his own obligation to live accordingly. He was intensely, scrupulously pious from then on, and it is inseparable from the science.

He was in Florence in 1642 when Galileo died, and read his work there.

The Irish rebellion of 1641 destroyed the family's revenues and stranded him abroad without money; he came home in 1644 to find his father dead and the country at war. He settled at Stalbridge in Dorset on an inherited manor and began experimenting.

The wealth is the enabling fact. Boyle never held a post, never taught, never needed a patron and never had to earn. He could buy instruments, employ assistants, publish at his own expense, and work on whatever he liked for as long as he liked. Almost nobody in the seventeenth century could do this.

In 1655 he moved to Oxford and took on a young assistant named Robert Hooke.

“I shall not dare to think myself a true naturalist till my skill can make my garden yield better herbs.”

— Robert Boyle, on the practical test of natural philosophy

Why this matters

Boyle's independence from patronage and employment let him publish freely and pursue experiments with no obligation to please anybody — a rare position in the seventeenth century.

You have the wealth and the storm in Geneva. What would you ask him?

Ask Boyle

• “What happened to you in that thunderstorm at Geneva?”
• “What did never needing money let you do?”
• “How did your father make his fortune?”
• “Do you see studying nature as a religious act?”
• “Why take on Hooke, and what did he do for you?”

Chapter 2 · The Bell That Could Be Seen and Not Heard

The air pump, and what happens when the air goes

1659 – 1660 · Oxford

Otto von Guericke in Germany had built a pump to evacuate a vessel. Boyle heard of it, and set Hooke to build a better one. Hooke did — the *machina Boyleana*, with a large glass receiver you could put things into and look at while the air was drawn out. It was probably the most sophisticated scientific instrument in Europe.

Boyle then put things in it. *New Experiments Physico-Mechanical, Touching the Spring of the Air* (1660) reports forty-three experiments.

A burning candle in the receiver goes out as the air is withdrawn. A bird placed in it becomes distressed and dies. So air is necessary both for a flame and for life — though Boyle could say nothing about *why*, since oxygen was over a century away. He suspected some particular ingredient of air was involved, and could not identify it.

The most elegant experiment is the bell. Suspend a bell inside the receiver, arranged so it can be struck from outside, and pump the air out. As the air thins, the sound fades, until at last the bell can be plainly *seen* to be ringing and cannot be heard at all.

Sound requires a medium. Light does not. That is demonstrated in one apparatus, visibly, in a way no argument could achieve — and it is still the clearest demonstration of the point available.

Thomas Hobbes attacked the whole programme, arguing that a vacuum is impossible and that the pump necessarily leaked, so the experiments proved nothing. The resulting dispute is one of the founding arguments about what an experiment can establish.

Why this matters

The bell in the evacuated jar shows in a single apparatus that sound needs a medium and light does not — a demonstration no argument could replace.

You have the candle, the bird and the silent bell. What is your question?

Ask Boyle

• “Why can the bell be seen ringing and not heard?”
• “What did you think air was doing for a candle?”
• “How did you answer Hobbes's charge that the pump leaked?”
• “How much of the pump was Hooke's work?”
• “Was killing a bird in the receiver necessary?”

Chapter 3 · The J-Shaped Tube

Volume against pressure, 1662

1662 · Oxford

The apparatus is beautifully simple. Take a glass tube bent into a J, with a long open arm and a short sealed one. Pour mercury into the long arm until it just fills the bend, trapping a column of air in the short sealed arm at ordinary atmospheric pressure.

Now pour in more mercury. The extra weight compresses the trapped air, and the difference in mercury levels between the two arms tells you how much extra pressure you have applied.

Measure the length of the trapped air column against the pressure. Double the pressure and the volume halves. Treble it and the volume falls to a third.

Volume varies inversely with pressure, at constant temperature. That is Boyle's law.

The caveats are worth being honest about. The law was suggested to Boyle by Richard Towneley and Henry Power, and Boyle credited them — he called it Towneley's hypothesis, and the attachment of his own name came later. Edme Mariotte published it independently in France in 1676 and added the temperature condition explicitly, which is why the French call it Mariotte's law.

Boyle's own explanation was mechanical: he pictured air as made of particles like tiny coiled springs or fleeces, which resist compression and push back. He called this the *spring of the air*. It is not the modern kinetic account — where pressure comes from moving particles striking the walls — but it is a genuine physical model rather than a bare formula.

The law fails at high pressures and low temperatures, where real gases depart from it. Boyle had no way of reaching those conditions.

Why this matters

Boyle's law is one of the first quantitative relationships in chemistry, and Boyle himself credited the hypothesis to Towneley rather than claiming it.

You have the mercury and the shrinking column of air. What would you ask?

Ask Boyle

• “Walk me through the J-tube experiment.”
• “What did you think was pushing back when you compressed the air?”
• “Why did you call it Towneley's hypothesis?”
• “Where does the law stop working?”
• “Why does temperature have to be held constant?”

Chapter 4 · The Sceptical Chymist

Attacking both sides at once

1661 · Oxford · London

*The Sceptical Chymist* was published in 1661, and its target is both of the available theories of matter.

Against Aristotle: the doctrine that everything is composed of earth, air, fire and water. Against the alchemists and Paracelsians: the doctrine that everything is composed of three principles — salt, sulphur and mercury.

Boyle's objection to both is the same and it is empirical. Neither list survives the fire assay. Heat a substance and see what comes off, and you do not get four things or three things. You get a different number for different substances, and you often get things that were not obviously in the original at all. The theories were arrived at first and the evidence fitted to them afterwards.

His alternative definition is the one that lasted. An *element* is a substance that cannot be decomposed further by any known means — and, crucially, whether something is an element is a matter for experiment, not for doctrine. You do not know in advance how many there are. You find out.

That is a shift from a philosophical question to an experimental one, and it is what made the eighteenth-century discovery of the actual elements possible.

It should be said that Boyle did not produce a list, and did not identify a single element himself.

And here is the complication. Boyle practised alchemy throughout his life. He believed transmutation of metals was possible, kept alchemical recipes, corresponded with practitioners, sought the philosophers' stone, and lobbied successfully for the repeal of the statute against multiplying gold. His scepticism was about the *theory*, not the project.

Why this matters

Boyle made the identity of the elements an experimental question rather than a doctrinal one, without identifying a single element himself.

You have the attack on both theories, and the alchemy. What is your question?

Ask Boyle

• “What is wrong with the four elements?”
• “How would you tell whether something is an element?”
• “How can you attack the alchemists and practise alchemy?”
• “Did you ever think you had transmuted anything?”
• “Why did you not try to list the elements yourself?”

Chapter 5 · Publish the Failures

The reporting standard, and a quiet death

1663 – 1691 · Oxford · London · Pall Mall

Boyle was a founding Fellow of the Royal Society in 1663 and did more than anyone to set its convention for reporting an experiment. The rule he argued for and practised: describe the apparatus fully, describe the procedure step by step, give the actual numbers, and *publish the attempts that failed*.

His reasoning was that a reader who is shown only the successful outcome cannot judge it. They do not know how often it worked, what conditions were needed, or whether the result was selected from a range. Without the failures, an experiment is a claim rather than evidence.

This is the ancestor of the modern methods section, and it is the practice that separates a scientific report from a testimonial. It is also, notably, a standard modern science is criticised for failing to keep — publication bias, the tendency to print positive results and bury negative ones, is a live problem, and Boyle identified the reason for the rule three hundred and fifty years ago.

He declined the presidency of the Royal Society because the oath was against his conscience, and refused a peerage.

He lived from 1668 in the Pall Mall house of his sister Katherine Jones, Lady Ranelagh — a formidable political and intellectual figure, at the centre of the Hartlib circle, and by every account his closest intellectual companion. They lived and worked together for over twenty years.

He was in poor health for most of his life, worked slowly, and kept a laboratory to the end. Katherine died on 23 December 1691. Boyle died a week later, on 31 December, aged sixty-four.

He left money to found the Boyle Lectures, for the defence of Christianity against unbelievers, which are still given.

Why this matters

Boyle argued that an experiment must be reported completely enough to be repeated, failures included, and that publishing only successes turns evidence into testimony.

You have the reporting standard and the house in Pall Mall. What would you ask?

Ask Boyle

• “Why publish the experiments that did not work?”
• “What does a reader lose when they only see the successes?”
• “Tell me about your sister Katherine.”
• “Why refuse the presidency of the Royal Society?”
• “What would you make of a journal that prints only positive results?”

What Boyle changed

Boyle's law is taught in every physics and chemistry course, and the bell-jar experiment remains the clearest demonstration that sound needs a medium. His larger legacy is procedural: the convention that an experiment must be reported fully enough for a stranger to repeat it, failures included, is substantially his, and it is what separates modern science from what preceded it. His definition of an element as whatever cannot be decomposed further made the identity of the elements an experimental question.

A debate that continues

The gas law was suggested by Towneley and Power and independently published by Mariotte, so the name is largely an accident of reputation; and Boyle practised alchemy and sought transmutation throughout the period in which he attacked alchemical theory.

Keep exploring — ask Boyle

• “What would you have put in the receiver next?”
• “Can a person hold two incompatible theories honestly?”
• “Which of your failed experiments taught you most?”

Related lives

• Robert Hooke — Who Named the Cell and Weighed the Spring
• Antoine Lavoisier — Father of Modern Chemistry
• Isaac Newton — Lucasian Professor · President of the Royal Society
• Joseph Black — Whose Thermometer Would Not Rise

Related themes

Gas laws and pressure · Elements and compounds · How experiments are reported