John Tyndall

• 1. Introduction

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  John Tyndall died on the 4th of December 1893 from an accidental overdose of chloral hydrate, administered by his own wife. As he realized what had happened, he turned to Louisa and said: "My darling, you have killed your John." It was the last sentence spoken by a man who had spent forty years teaching the world to see the invisible: the heat hiding inside molecules, the scatter of light through dusty air, the slow creep of glaciers down a mountain. He was 73. His wife survived him by nearly half a century, outliving him long enough to finally authorize a biography she had spent decades avoiding finishing.

  Tyndall was born on the 2nd of August 1820 in Leighlinbridge, County Carlow, Ireland, to a police constable whose family traced its roots to Gloucestershire emigrants who had settled in southeast Ireland around 1670. That Irish upbringing, that constable's-son resourcefulness, and a friendship formed at a boarding school in Hampshire would eventually carry him from a drafting table at the Ordnance Survey to the front pages of newspapers in Britain, Ireland, and North America. The questions worth sitting with are these: how did a draftsman become the man who first proved the greenhouse effect? And how did the same person become one of the most widely read science writers of the nineteenth century?

• 2. From Draftsman to Marburg

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  Tyndall's first job was drawing maps. Hired by the Ordnance Survey of Ireland in 1839, he moved to the Ordnance Survey for Great Britain in 1842. The 1840s brought a railway-building boom, and his land surveying skills were in high demand; between 1844 and 1847 he was lucratively employed in railway construction planning. When that work slackened, he chose to become a mathematics and surveying teacher at Queenwood College, a boarding school in Hampshire. He later recalled: "the desire to grow intellectually did not forsake me; and, when railway work slackened, I accepted in 1847 a post as master in Queenwood College."

  At Queenwood he met Edward Frankland, a young chemistry teacher who had previously worked as a laboratory assistant for the British Geological Survey. The two became close friends. Frankland knew that certain German universities were far ahead of anything in Britain in experimental chemistry and physics, and the pair moved to Germany together in the summer of 1848. They enrolled at the University of Marburg, drawn by the reputation of Robert Bunsen as a teacher. Tyndall studied under Bunsen for two years, but the figure who left the deeper mark was Professor Hermann Knoblauch, with whom Tyndall kept up a correspondence by letter for many years after leaving.

  Tyndall's Marburg dissertation, completed in 1850 under Friedrich Ludwig Stegmann, was a mathematical analysis of screw surfaces. He then stayed in Germany for a further year, doing research on magnetism with Knoblauch and spending several months at the Berlin laboratory of Knoblauch's own teacher, Heinrich Gustav Magnus. Both Bunsen and Magnus were, as the record makes clear today, among the finest experimental science instructors of the era. When Tyndall returned to England in the summer of 1851, he arrived with arguably the best experimental science education available to anyone in the country.

• 3. Magnetic Polarity and the Royal Institution

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  Tyndall's first original research in physics focused on magnetism and diamagnetic polarity, work he pursued from 1850 to 1856. His two most influential early papers were co-authored with Knoblauch; the first of them, dated May 1850, was titled "The magneto-optic properties of crystals, and the relation of magnetism and diamagnetism to molecular arrangement." The experiments and the interpretation were considered inspired by contemporaries, and the reports made Tyndall known quickly among the leading scientists of the day. He was elected a Fellow of the Royal Society in 1852.

  Gaining that recognition opened the right doors. When searching for a research appointment, Tyndall was able to ask Poggendorff, the longtime editor of the leading German physics journal, along with other prominent figures, to write testimonials on his behalf. In 1853, he was appointed Professor of Natural Philosophy at the Royal Institution in London. The appointment owed no small amount to the esteem his magnetic work had earned from Michael Faraday, who led magnetic investigations at the Royal Institution. A decade later, Tyndall was appointed to the positions Faraday had held when Faraday retired, holding the professorship there from 1853 to 1887.

  His election as a member of the American Philosophical Society came in 1868, one of several international recognitions that tracked his expanding scientific reputation. The Royal Institution would also be where Tyndall famously demonstrated the propagation of light down a falling stream of water through total internal reflection, a demonstration his audiences called the "light fountain." Jean-Daniel Colladon had published a description of this phenomenon in Comptes Rendus in 1842, and there is suggestive evidence that Tyndall's knowledge of it came from Colladon's work. There is no evidence Tyndall ever claimed to have originated it himself.

• 4. The Greenhouse Effect, Proved

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  Glaciology pointed Tyndall toward one of the most consequential discoveries in the history of physics. Studying glaciers had drawn his attention to the research of Horace Bénédict de Saussure into how sunlight heats surfaces, and to a concept developed by Joseph Fourier and extended by Claude Pouillet and William Hopkins: that visible solar heat penetrates the atmosphere more easily than the infrared radiation emitted back from the warmed Earth, causing what we now call the greenhouse effect.

  In the spring of 1859, Tyndall began research into how thermal radiation, both visible and infrared, interacts with different gases and aerosols. He developed differential absorption spectroscopy using the electro-magnetic thermopile devised by Macedonio Melloni. He began intensive experiments on the 9th of May 1859, at first without significant results, then improved the apparatus and on the 18th of May wrote in his journal: "Experimented all day; the subject is completely in my hands!" On the 26th of May he sent the Royal Society a note stating that virtually nothing had previously been published on the transmission of radiant heat through gaseous bodies.

  On the 10th of June he demonstrated his results in a Royal Society lecture. Coal gas and ether, he showed, strongly absorbed infrared radiant heat. He described the mechanism directly: solar heat crosses the atmosphere, but "when the heat is absorbed by the planet, it is so changed in quality that the rays emanating from the planet cannot get with the same freedom back into space. Thus the atmosphere admits of the entrance of solar heat; but checks its exit, and the result is a tendency to accumulate heat at the surface of the planet."

  His measurements identified water vapour as the strongest absorber of radiant heat in the atmosphere and its principal temperature controller. He was the first to correctly measure the relative infrared absorptive powers of nitrogen, oxygen, water vapour, carbon dioxide, ozone, methane, and other trace gases. Three years before his work, in 1856, the American scientist Eunice Newton Foote had demonstrated that water vapour and carbon dioxide absorb heat from solar radiation, but she had not differentiated the effects of infrared. Tyndall, in 1860, was also the first to demonstrate and quantify that visually transparent gases emit infrared radiation. His main reports from the 1860s were republished as a 450-page collection in 1872 under the title Contributions to Molecular Physics in the Domain of Radiant Heat.

• 5. The Alps and the Glacier Dispute

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  Tyndall first visited the Alps in 1856 for scientific reasons and found himself drawn back almost every summer afterward as both researcher and climber. He was a member of the first team to reach the summit of the Weisshorn in 1861, and he led one of the early teams to reach the top of the Matterhorn in 1868. His name sits among those associated with what historians call the "Golden age of alpinism," the mid-Victorian years when the most difficult Alpine peaks were summited for the first time.

  His scientific interest in the mountains centred on glaciers and how they move. That inquiry pulled him into a prolonged and bitter dispute with James David Forbes. Much of the foundational work on glacier motion had been done by Forbes, but Forbes was unaware of regelation, a phenomenon discovered by Michael Faraday. Regelation played a central role in Tyndall's explanation of glacial flow, and Forbes rejected that framing entirely. A secondary dispute then broke out publicly over who deserved credit for what.

  Tyndall laid out his own accounting of the credits with notable specificity: "The idea of semi-fluid motion belongs entirely to Louis Rendu; the proof of the quicker central flow belongs in part to Rendu, but almost wholly to Louis Agassiz and Forbes; the proof of the retardation of the bed belongs to Forbes alone; while the discovery of the locus of the point of maximum motion belongs, I suppose, to me." The quarrel did not end with either man's death; their respective biographers continued it on their behalf, without reaching agreement. Numerous landforms carry Tyndall's name today, including the Tyndall Glacier in Chile, the Tyndall Glacier in Colorado, the Tyndall Glacier in Alaska, Mount Tyndall in California, and Mount Tyndall in Tasmania.

• 6. Germs, Spores, and Tyndallization

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  One of the stranger detours in Tyndall's career began with a need for clean air. His radiant heat experiments required air from which all floating particles had been removed, and he developed a simple method: a wooden box coated inside with sticky glycerin. After a few days, all particulates settled onto the glycerin-coated walls and floor. When he examined the remaining air with strong light beams, nothing scattered, and there were no signs of floating micro-organisms.

  Tyndall boiled meat broths to sterilize them and then left them sitting in this optically pure air. They remained, as he put it, "sweet" to smell and taste after many months. Broths left in ordinary air turned putrid within days. This extended Louis Pasteur's earlier demonstrations that micro-organisms drive decomposition, and during the mid-1870s Pasteur and Tyndall were in frequent communication.

  The following year, 1876, some of Tyndall's supposedly heat-sterilized broths rotted even in optically pure air. Investigating the failure, he traced contamination to dry bacterial spores from hay in the laboratory. He correctly concluded, citing research by Ferdinand Cohn, that while simple boiling kills all bacteria, bacterial spores can survive it. He devised a method of repeated heating at intervals to eradicate the spores, which came to be known as Tyndallization. At the time, it historically was the earliest known effective means of destroying bacterial spores, and it helped vindicate the germ theory against critics whose own experiments had failed for exactly the same reason. Tyndall also invented a fireman's respirator in 1871, a hood designed to filter smoke and noxious gas, with improvements in 1874; and, from his work measuring carbon dioxide in exhaled human breath in 1862 and 1864, he developed a system whose basic principles are used in hospitals today to monitor patients under anaesthesia, a field now called capnometry.

• 7. Teaching the Invisible World

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  From the mid-1860s onward, Tyndall was among the most famous living physicists in the world, and he earned that position as much through teaching as through research. He gave hundreds of public lectures at the Royal Institution to non-specialist audiences. A London publication in 1878 described the result plainly: "When he lectures at the Royal Institution the theatre is crowded." His 1872 lecture tour of the United States drew large paying crowds of non-scientists who came to hear him speak about the nature of light. He donated the entire net proceeds of that tour to a trustee for the purpose of fostering science in America.

  His books reached the largest audience of all. He published more than a dozen, most of them not written for experts. The three longest tutorials, Heat (1863), Sound (1867), and Light (1873), represented state-of-the-art experimental physics at the time of writing, and they made recent major innovations accessible to general readers for the first time. Heat: a Mode of Motion ran to at least 550 pages, remained in print for at least 50 years, and is still in print today. James Clerk Maxwell wrote in 1871 that in it "the doctrines of the science are forcibly impressed on the mind by well-chosen illustrative experiments." Earlier editions of Sound were translated into Chinese at the expense of the Chinese government, and translated into German under the supervision of Hermann von Helmholtz.

  Tyndall's closing remarks at the end of The Forms of Water (1872), a tutorial written for a "youthful audience," give a precise picture of how he understood the relationship between teacher and student: "Here, my friend, our labours close. It has been a true pleasure to me to have you at my side so long. In the sweat of our brows we have often reached the heights where our work lay, but you have been steadfast and industrious throughout, using in all possible cases your own muscles instead of relying upon mine." His index entry across 19th-century scientific research journals lists more than 147 papers, with practically all of them dated between 1850 and 1884, averaging more than four papers a year across that 35-year span.

• 8. Science, Religion, and Irish Politics

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  Most of the leading British physicists of Tyndall's generation were religious conservatives who believed science and faith were harmonious. James Joule, Balfour Stewart, James Clerk Maxwell, George Gabriel Stokes, and Lord Kelvin all investigated heat or light contemporaneously with Tyndall and held that view. Tyndall held the opposite, and he held it publicly.

  Tyndall first met the anatomist Thomas Henry Huxley in 1851, and the two maintained a lifelong friendship within a circle that included the chemist Edward Frankland, the mathematician Thomas Archer Hirst, and the social philosopher Herbert Spencer. All of them vocally supported Charles Darwin's theory of evolution and worked to sharpen the boundary between science and religion.

  As the elected president of the British Association for the Advancement of Science in 1874, Tyndall gave a keynote address in Belfast that traced the history of evolutionary theories favourably, mentioned Darwin's name more than 20 times by name, and concluded by asserting that religious sentiment should not be permitted to intrude "on the region of knowledge, over which it holds no command." Newspapers in Britain, Ireland, North America, and on the European Continent carried the speech on their front pages. The scrutiny that followed helped bring the evolutionist philosophical position closer to mainstream acceptance.

  In Ireland the politics were sharper. Between 1886 and 1893, Tyndall was active in the debate over Irish Home Rule, opposing it as did the great majority of Irish-born scientists of the century. In an opinion piece published in The Times on the 27th of December 1890, he described the Catholic clergy as "the heart and soul of this movement" and called the prospect of placing the non-Catholic minority under their dominion "an unspeakable crime." He attempted without success to persuade Britain's premier scientific society to denounce Home Rule as contrary to the interests of science. Late in life, his charitable donations went most visibly to the Irish Unionist political cause. When he died, his estate was valued at £22,122; for comparison, a police constable in London at the time earned about £80 per year. A memorial erected at 2340 metres above the village of Belalp, in sight of the Aletsch Glacier, now marks the mountain slopes above the holiday chalet he and Louisa built there in 1877.