John Tyndall

Chapter 1 · From a Railway Cutting to the Royal Institution

A constable's son, and physics learned in Germany

1820 – 1853 · County Carlow · Preston · Queenwood · Marburg · London

John Tyndall was born at Leighlinbridge in County Carlow in August 1820, the son of a *police constable* who had been a shoemaker. The family were Protestants of modest means in a poor country, and there was no money for a university.

He joined the *Ordnance Survey* of Ireland as a surveyor at nineteen, and then worked on the *railway boom* in England — surveying routes across Lancashire and Yorkshire in the 1840s, a hard practical training in measurement, drawing and getting numbers right in bad weather.

He was dismissed from the Ordnance Survey after protesting publicly about the treatment of Irish staff compared with English, which is early evidence of a temperament that stayed with him.

He then taught mathematics and surveying at *Queenwood College* in Hampshire, a school of unusual character run on Quaker and cooperative lines, where he met the chemist *Edward Frankland*.

In 1848, aged twenty-eight, he and Frankland went to *Marburg* in Germany, at their own expense, to get a proper scientific education. German universities were far ahead of British ones in laboratory training, and Tyndall took his doctorate there in two years under *Robert Bunsen* and *Karl Knoblauch*.

He came back with a German doctorate, no money and no position, and spent a difficult period before a lecture at the *Royal Institution* in 1853 was so successful that he was appointed Professor of Natural Philosophy there.

He worked alongside *Michael Faraday*, whom he revered, and succeeded him as *Superintendent* in 1867.

So he went from a railway cutting to Faraday's chair in about fifteen years, without money or connections.

“The brightest flashes in the world of thought are incomplete until they have been proved to have their counterparts in the world of fact.”

— John Tyndall, Fragments of Science

Why this matters

Tyndall came to physics through railway surveying and paid for his own German doctorate, and the practical measuring habits show throughout his work.

You have the survey chains and the Marburg laboratory. What would you ask him?

Ask Tyndall

• “Why go to Germany at your own expense?”
• “What did surveying teach you that a laboratory would not?”
• “Why were you dismissed from the Ordnance Survey?”
• “What was it like working alongside Faraday?”
• “How does a poor Irishman get a chair in London?”

Chapter 2 · Light Round a Bend

1854, and the principle of the optical fibre

1854 · London · The Royal Institution

The demonstration is simple and it looks like magic.

Take a vessel of water, with a hole in its side near the bottom. Water arcs out through the hole and falls in a curve. Light the vessel from behind so that a beam shines through the water and out through the hole.

The light does not continue in a straight line. It *travels down the arc of falling water* and emerges at the bottom, so that the falling stream *glows* along its whole length.

The reason is *total internal reflection*. Light travelling inside water and striking the surface from within is refracted out — unless it strikes at a shallow enough angle, beyond the *critical angle*, in which case it is *entirely reflected back inside*.

Because the stream curves *gently*, the light meets the inside surface at a very oblique angle at every point along it. So it is reflected back in, again and again, hundreds of times, and cannot escape until the stream breaks up.

The light is *trapped* in the water and follows wherever it goes.

That is the principle of the *optical fibre*. A glass fibre works exactly the same way: light enters at one end, strikes the walls too obliquely to escape, and is reflected along the length of the fibre round whatever bends it takes.

Every undersea cable, every fibre broadband connection, every endoscope and every fibre-optic sensor works on the effect Tyndall showed to a lecture theatre in 1854.

The priority should be stated honestly. *Daniel Colladon* in Geneva had demonstrated it in 1842, and *Jacques Babinet* had reported something similar earlier. Tyndall knew of Colladon's work and did not always make the debt plain, and he is sometimes credited with a discovery that was not his.

What is his is the *demonstration* — done in front of large audiences, repeatedly, so memorably that it entered the general knowledge of the subject.

Why this matters

Light trapped in a curved stream of water by total internal reflection is exactly the principle of every optical fibre in the world.

You have the glowing arc of water. What is your question?

Ask Tyndall

• “Why does the light follow the water instead of going straight?”
• “What is a critical angle?”
• “How is this the same as a fibre-optic cable?”
• “Did you credit Colladon properly?”
• “Why does a demonstration matter more than a paper?”

Chapter 3 · Which Gases Trap the Heat

1859, and the first measurements of the greenhouse effect

1859 – 1861 · London

Tyndall's most important research is on the absorption of *radiant heat* by gases, and it is the experimental foundation of climate science.

The question came from *glaciers*. Tyndall was a serious alpinist and had studied glacier motion; the *ice ages* were then a live problem, and the question of why the Earth's climate changes was open. *Joseph Fourier* had argued in the 1820s that the atmosphere must retain heat somehow, and *Eunice Foote* in America had shown in 1856 that a jar of carbon dioxide in sunlight gets hotter than a jar of air.

Nobody had *measured which gases do it, and how much*.

Tyndall built the apparatus. A long brass tube, sealed with rock-salt windows — rock salt because ordinary glass absorbs infrared and would ruin the measurement. A source of radiant heat at one end. A sensitive *thermopile* at the other, connected to a galvanometer, measuring how much heat gets through.

Evacuate the tube, measure. Admit a gas, measure again. The difference is what the gas absorbs.

The results were decisive.

*Oxygen* and *nitrogen* — which are ninety-nine per cent of the atmosphere — are almost *completely transparent* to radiant heat. They absorb essentially nothing.

*Water vapour*, *carbon dioxide*, *methane* and other minor constituents absorb it *strongly*.

So the heat-trapping capacity of the atmosphere belongs almost entirely to gases present in *tiny* quantities. Tyndall wrote that water vapour is a blanket more necessary to the vegetable life of England than clothing is to man, and that removing it for a single summer night would destroy every plant a frost can kill.

He understood the implication: a change in these trace gases would change the climate, and he suggested it as a cause of the ice ages.

That is the greenhouse effect, measured in 1859. Arrhenius calculated the magnitude in 1896.

Why this matters

The gases that trap the Earth's heat are present in tiny quantities, and the ninety-nine per cent of the atmosphere that is oxygen and nitrogen does essentially nothing.

You have the brass tube and the transparent bulk of the air. What would you ask?

Ask Tyndall

• “Why rock-salt windows rather than glass?”
• “Which gases absorb radiant heat and which do not?”
• “Why is it surprising that trace gases do the work?”
• “What made you think about the ice ages?”
• “What did Eunice Foote find three years earlier?”

Chapter 4 · A Blue Sky in a Glass Tube

Scattering, dust-free air, and Pasteur

1868 – 1877 · London

Tyndall investigated why the *sky is blue*, and he made one on a lecture bench.

He passed a beam of white light through a long tube containing a fine mist of particles produced by the decomposition of a vapour. Viewed *from the side*, the tube glowed *blue*, because small particles scatter *short* wavelengths — blue — far more than long ones. Viewed *end on*, looking through the tube toward the light, it appeared *red*, because the blue had been scattered out and only the longer wavelengths came through.

A blue sky and a red sunset, in a glass tube, from one cause.

The *Tyndall effect* is the name for the scattering of light by particles in a colloid, and it is why a beam is visible in a dusty room, why headlights show in fog, and why the sky is blue at all — though the sky's blue is chiefly due to scattering by the *molecules* of the air themselves, as Rayleigh established, rather than by dust.

The investigation led somewhere unexpected.

To do the experiments properly Tyndall needed *dust-free air*, and he worked out how to get it: leave air standing in a sealed chamber for long enough and the dust settles, at which point a light beam passed through it becomes *invisible* because there is nothing to scatter it.

He then noticed something. Sterilised broth left open to *ordinary* air went putrid. Sterilised broth left open to *optically dust-free* air did *not*.

So whatever causes putrefaction is *carried on the dust*, not present in the air itself.

That is powerful support for *Pasteur* and germ theory, against spontaneous generation, and Tyndall became Pasteur's most effective advocate in Britain — publishing, lecturing and arguing the case in public against *Henry Charlton Bastian* and the spontaneous-generation party.

He also developed *tyndallisation*: repeated gentle heating on successive days, which kills bacteria in the vegetative state, allows any surviving spores to germinate between heatings, and then kills those too — a method for sterilising things that boiling would spoil.

Why this matters

Broth exposed to optically dust-free air does not putrefy, which shows that what causes decay is carried on dust rather than present in air itself.

You have the blue tube and the broth that stayed clean. What is your question?

Ask Tyndall

• “Why does scattering make a blue sky and a red sunset?”
• “How do you make air optically dust-free?”
• “What did the broth experiments prove?”
• “What is tyndallisation and why does it work?”
• “Is the sky blue because of dust?”

Chapter 5 · The Belfast Address

A public quarrel, and an accidental death

1874 – 1893 · Belfast · London · Hindhead

Tyndall was a public figure, and in 1874, as President of the *British Association*, he delivered his presidential address in *Belfast*.

It is one of the most controversial scientific speeches of the nineteenth century. Tyndall argued that science must be free to investigate *any* question about the material world, without deference to theology, and traced a materialist intellectual tradition from the Greek atomists to Darwin. He said, in effect, that theology must relinquish all claims over the domain of natural knowledge.

Delivered in *Belfast*, in 1874, in a city divided along religious lines, this caused an uproar. Catholic and Protestant clergy denounced it from pulpits. It was attacked in the press across Britain and Ireland for months.

Tyndall did not retreat. He belonged to the *X Club* — a dining group of nine scientists including *Thomas Huxley*, *Joseph Hooker* and *Herbert Spencer* — who worked deliberately to professionalise British science and reduce clerical influence over it. The Belfast Address was that campaign at its most confrontational.

It cost him. It hardened opposition, damaged his standing with parts of the public, and he was drawn into further controversies afterwards.

He also did a great deal of practical work. He investigated *lighthouse* illumination and *fog signals* for Trinity House, and helped establish how far and how reliably a warning sound carries at sea. He worked on the *acoustics* of the atmosphere.

He was a serious *alpinist* — among the first to climb the *Weisshorn* in 1861, and made an early attempt on the Matterhorn — and studied glaciers on the ground, arguing with Forbes about how ice flows.

He married *Louisa Hamilton* in 1876, when he was fifty-five and she thirty. They retired to Hindhead in Surrey.

On 4 December 1893 Louisa, confusing two bottles, gave him an overdose of *chloral hydrate*, which he took for insomnia. She realised immediately. He said to her that his poor darling had killed her John, and died some hours later, aged seventy-three.

She survived him by *forty-seven years*, spending much of that time on a biography of him that she never finished.

Why this matters

The Belfast Address was a deliberate campaign to free scientific inquiry from clerical authority, and it cost Tyndall considerable public standing.

You have the address, the mountains and the two bottles. What would you ask?

Ask Tyndall

• “What did you actually say at Belfast?”
• “Was it wise to say it in Belfast in 1874?”
• “What was the X Club trying to do?”
• “Why go up mountains to study ice?”
• “What did the lighthouse work involve?”

What Tyndall changed

The guided light beam Tyndall showed to a lecture theatre is the principle of every optical fibre in the world. His measurements of which atmospheric gases absorb radiant heat are the experimental foundation of climate science, and his dust-free air experiments gave decisive support to germ theory in Britain. The Tyndall effect is named after him.

A debate that continues

Daniel Colladon demonstrated the guided water jet in 1842 and Tyndall did not always make the debt plain; and Eunice Foote had shown carbon dioxide's heat-trapping property in 1856, three years before his measurements, and was long overlooked.

Keep exploring — ask Tyndall

• “What should a scientist demonstrate rather than argue?”
• “Would you give the Belfast Address again?”
• “What did the glaciers tell you about climate?”

Related lives

• Michael Faraday — Discoverer of Electromagnetic Induction
• Louis Pasteur — Father of Germ Theory
• Svante Arrhenius — Whose Thesis Nearly Failed
• Robert Bunsen — Who Gave the Flame a Collar

Related themes

Total internal reflection · The greenhouse effect · Scattering of light