Eunice Foote, John Tyndall and a question of priority

Introduction

It has generally been accepted that John Tyndall (ca1822–1893) was the first person to demonstrate the absorption of radiant heat by water vapour and carbon dioxide, underpinning our current understanding of the greenhouse effect, climate change, weather and meteorology. Yet it is now clear that an American woman, Eunice Foote, made a similar discovery in 1856, three years before Tyndall.¹ In addition, she suggested that variations in the amounts of water vapour and carbon dioxide in the atmosphere could cause changes in climate. Tyndall made this suggestion also, in his seminal paper in 1861.² He is viewed, in the light of his discoveries, as one of the founders in climate science. Did he know about Eunice Foote's work?

Eunice Foote

Eunice Foote, née Newton (1819–1888) was a scientific researcher, inventor and women's rights campaigner. Her husband, Elisha (1809–1883), whom she married in 1841, specialized in patent law, and became a judge. Both Eunice and Elisha took out patents on inventions. Eunice attended the Seneca Falls Convention in 1848, the first women's rights convention, and was one of the signatories to the Convention's Declaration of Sentiments.³

In August 1856, some experiments of Eunice Foote on the effect of solar radiation on gases enclosed in cylinders were reported in an oral presentation to the Annual Meeting of the American Association for the Advancement of Science (AAAS), held that year in Albany, New York. Her paper was published in the American Journal of Science and Arts the same year as ‘Circumstances affecting the heat of the Sun's rays’ (Figure 1),⁴ immediately following a longer paper by her husband.⁵ In this latter paper, Elisha reported experiments on the temperatures recorded by differential thermometers exposed to the sun, outside or inside a room, at varying ambient air temperatures. The ambient temperature appeared to affect the temperatures recorded. Eunice's experiments explored the effect of exposing tubes containing different gases to the sun. Not only did she demonstrate the absorption of heat from solar radiation by carbon dioxide and water vapour (with a proviso described below), but she also posited a direct connection to their variability as a possible cause of climate change. Her paper was read to the meeting by Joseph Henry (then the founding director of the Smithsonian Institution). Elisha had read his own paper. Eunice did not read her paper. It was possible, though uncommon, for women to speak at AAAS meetings. Women could be members of the AAAS, though she was not, and she may have been present with her husband.

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Foote's experimental apparatus was simple: a (presumed; the material is not specified) glass cylinder 4 inches in diameter and 30 inches in length, in which thermometers were placed. Her experimental arrangement, though poorly described and not illustrated, is much like Saussure's heliothermometer of the late 1700s, being an enclosed arrangement on which solar radiation is brought to bear. The warming effect in the enclosure was already known, and Saussure had used this to demonstrate an appreciable increase in solar heat with altitude.⁶ But the specific result with carbon dioxide and moist air (and with condensed compared to rarefied air) was not known, and that is Foote's unique contribution. However, her experimental arrangement does not differentiate between the direct effect of solar radiation and that (in modern terms) of radiated longwave infra-red from the earth's surface. Tyndall's apparatus only uses longwave infra-red (from a Leslie cube at 100°C), and therefore effectively establishes the physical basis of what we now call the greenhouse effect, which is initiated by longwave radiation from the earth's surface (although the average temperature of the earth's surface is lower, at around 15°C). As Katharine Hayhoe and Joshua Halpern have pointed out, Foote's experiments could not do that.⁷ Nevertheless, without specifying the exact protocols, Foote does describe experiments carried out in the shade as well as in direct sunlight, showing similar, but less marked, results. Depending on the nature of her glass, and its infra-red cut-off,⁸ neither of which we know, she may also have unwittingly detected the basis of the greenhouse effect.

Foote does seem to have been the first person to notice the ability of carbon dioxide and water vapour to absorb heat, and to make the direct link between the variability of these atmospheric constituents and climate change. For that she deserves proper recognition, even if she was not able to explore, and perhaps did not recognize, the distinction between solar radiation and radiated heat from the earth.

John Tyndall

Unlike Eunice Foote—an amateur American woman in a country without much scientific infrastructure—Tyndall had taken a doctorate at the University of Marburg, and then worked in Marburg, Berlin and London with some of the greatest experimental physicists of the day. He had access to the latest apparatus, and to the skilled instrument-makers who could produce accurate equipment to his specifications. Tyndall had already made a name for himself in his work on diamagnetism⁹ and on the structure and motion of glaciers.¹⁰ Several strands of thought drove him now to explore the absorption of heat by gases, including his experiences in the Alps. As he reported in his first major paper on the subject:

He had read Macedonio Melloni's work on the absorption of heat by liquids and solids around 1850,¹² and frequently discussed the issue with friends. Now he aimed to do for gases what Melloni had done for liquids and solids. He approached the topic with his already formed view that the structure of matter—and he believed in the real existence of atoms and molecules—was important in determining its interaction with ‘force’ (or energy as we would now term it), whether in the form of magnetism or of heat. He was convinced that not only the physical but also the chemical composition of substances, and specifically their molecules, played a part previously unrecognized in radiation and absorption.¹³ He would be probing the nature of molecules themselves using radiation. It was a research programme driven by a clear physical imagination.

Tyndall's experimental approach differs substantially from Foote's, in two respects. First, while Foote was exposing gases in (presumed) glass cylinders to the full spectrum of solar radiation, Tyndall's heat source was a Leslie cube containing boiling water at 100°C. In modern terms, Tyndall was examining longwave infra-red, while Foote made use of the whole solar spectrum incident at ground level (with the exception of her experiments in the shade). Second, Tyndall's invention of his differential spectrometer (Figure 2) gave him a sensitive and accurate means of determining very small amounts of absorption, and of measuring accurately the differences in absorption between different gases and of gases at different densities. Foote's was much less sensitive or accurate.

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In a familiar pattern in the history of science, several people were approaching this challenge at a similar time in different ways, and largely without each other's knowledge. In addition to Foote and Tyndall, the Germans Rudolf Franz and Gustav Magnus were also engaged.¹⁴ Tyndall referred to the work of Franz in his 1861 paper, which he rightly criticized for its experimental arrangement. He did not become aware of Magnus's work until Magnus wrote to him on 17 March 1861, nearly two years after Tyndall had published his initial results, and he immediately replied to secure his priority.¹⁵ Though it became clear that Tyndall had both started his work and published initial results before Magnus, without Magnus being aware of it nearly two years later, their friendly dispute about the ability of water vapour to absorb radiant heat would run until Magnus's death in 1870 and beyond. Nowhere does Tyndall, or Magnus, apparently refer to the work of Foote. Foote refers to no-one, so we are unable to tell what stimulated her work, though it extended that of her husband, who gave a limited rationale of investigating ‘the heat in the sun's rays’, and based his work on the use of an arrangement like John Leslie's differential thermometer in his exploration of solar heat. The only explanation Foote gave in her paper of the basis for her experiments was: ‘My investigations have had for their object to determine the different circumstances that affect the thermal action of the rays of light that proceed from the sun.’¹⁶

Sequence of events

Tyndall made his initial discovery of the absorption of radiant heat by gases on 18 May 1859, after only a few days’ work.¹⁷ Realizing its significance, he announced it in outline almost immediately to the Royal Society, and in a Discourse at the Royal Institution.¹⁸ Keen to establish his priority, he ensured that reports were also published in Continental journals, including Cosmos, Il Nuovo Cimento and the Bibliothèque Universelle.¹⁹ It was only in the last of those that he specifically mentioned his discovery of the absorption of heat by water vapour and carbon dioxide. He made no mention of the climate. Given other commitments, it was not until later in 1860 that he carried out the further extensive series of experiments which were reported in his seminal paper and in the Bakerian Lecture to the Royal Society in early 1861.²⁰

Eunice Foote's work was noticed to an extent in America immediately after the presentation to the AAAS in 1856. John Perlin, who has explored her work in detail, has identified reports in a number of places, including the New York Daily Tribune,²¹ the Canadian Journal of Industry, Science and Art,²² and Scientific American.²³ It seems unlikely that such reports would be much read in Britain and Europe, and no such general coverage has yet been found on the eastern side of the Atlantic. The New York Daily Tribune article is significant, in that it reports that Joseph Henry said of Foote's results, … ‘that although the experiments were interesting and valuable, there were [many] [difficulties] encompassing [any] attempt to interpret their significance’.²⁴ Henry does not appear to have appreciated the importance of the work (none of his own research was in this field), and this may partly explain why he did not, as far as we know, promote it anywhere. Eunice Foote, as an amateur woman without an extensive network to the men of science, and with many other interests, was not in a position to do so herself. Tyndall and Henry knew each other only later. Extant letters between them, about 40 in total, date from the early 1870s. None mentions Foote in retrospect.²⁵

However, we do know of two reports of Foote's work that appeared in Europe, and could therefore have been noticed by physicists interested in the topic. Two short summaries of Foote's 1856 paper appeared in Britain and on the Continent: in the Edinburgh New Philosophical Journal for 1857,²⁶ and in the Jahresbericht for 1856 (also published in 1857).²⁷ No re-publications of the paper itself have yet been found in British or European journals, although the 1856 paper by Elisha Foote (Eunice's husband), which appeared immediately before Eunice's paper in the American Journal of Science and Arts, was republished in the Philosophical Magazine in 1857.²⁸ His paper, in hindsight, is much less significant than hers. Whoever selected it could hardly have failed to notice Eunice's paper, which starts on the facing page to the end of Elisha's, but did not select it. Did whoever selected Elisha's paper note the author's female name on the subsequent paper and skip straight over it? Nevertheless, we do know that an 1857 paper by Eunice was republished in the Philosophical Magazine in 1858.²⁹ That paper is about electrical excitation, not solar heat (and, according to the Royal Society's Catalogue of Scientific Papers, 1800–1900, it appears to be her last publication in physics). It is even possible that one or both of these papers was selected by Tyndall, as he was one of the five editors of the Philosophical Magazine at the time, though William Francis was the active managing editor. The plot thickens.

Who noticed Foote's paper?

We do not know for certain the identity of the people who selected Foote's paper and summarized it for the Edinburgh New Philosophical Journal and the Jahresbericht, nor who selected Elisha's paper for the Philosophical Magazine. Indeed, the summary for the Edinburgh New Philosophical Journal was made from newspaper reports as the conference paper was not available.³⁰ For the Jahresbericht, the summaries on heat were made by either Friedrich Zamminer or Hermann Kopp.³¹ Neither was a correspondent of Tyndall, as far as we know, though Tyndall had translated a paper of Kopp's for the Philosophical Magazine in 1852, one of many that he brought to the attention of British readers in this period.³²

The eight-line summary of Elisha's and Eunice's 1856 papers, which appeared in the Edinburgh New Philosophical Journal for 1857, reads in full as follows:

This summary describes Eunice's results with moist air and carbon dioxide, while not clearly attributing them to Eunice, but omits her direct conclusions about the atmosphere and climate. She is identified as ‘Mrs Elisha Foote’. The published paper (which was not available to the summarizer) gives her name as ‘Eunice Foote’.

The other eight-line summary of Eunice's 1856 results, which appeared in German in the Jahresbericht for 1856 (published in 1857), within a large section of 45 pages of summaries of studies on the physics of heat, reads as follows:

This summary also omits the direct conclusions about the atmosphere and climate, but at least has the grace to attribute the results to Eunice.

The real significance of her paper therefore seems to have gone unnoticed, or at least unremarked, by whoever wrote the summaries. In addition, we do not know who read the summaries, or indeed the original papers. The American Journal of Science and Arts was taken at the Royal Institution and elsewhere in Britain and in Europe. Presumably at least some people saw the original paper. Yet the people who summarized it seem to have missed its significance, as Henry did. Others also missed the reports of related new work. The well-connected Magnus, who was himself carrying out experiments in Berlin like Tyndall's (and later strongly challenged Tyndall on the absorption of heat by water vapour), had not even heard of Tyndall's initial results more than a year after their publication in Britain, France, Italy and Switzerland (the note was not published in German until 1861, in Die Fortschritte der Physik im Jahre 1859).³⁵ It would seem that he had also not registered the report of Foote's work in the Jahresbericht in 1857 either. We have the correspondence between Magnus and Tyndall about their experiments, and their chronologies, but it contains no mention of Foote.³⁶ It would also appear that other significant physicists were unaware of Foote's work. George Stokes and William Thomson (later Lord Kelvin) refereed Tyndall's major 1861 paper, in which he gave the first detailed account of his findings and made his climate change statements. Had they known of her work, they would surely have mentioned her. Indeed, Thomson in his note to Stokes said he thought Tyndall's results were ‘perfectly novel’ as far as he knew.³⁷ No mention of Foote has yet been found in the correspondence, journals or published papers of the critical physicists of the period. On the face of it, the significance of the paper passed everyone by who could have had a particular interest in it.

Did Tyndall notice Foote's paper?

Even if it was not brought directly to his attention, and there is no evidence from his private correspondence or his journals that it was, Tyndall could have seen the paper in the American Journal of Science and Arts, or the two summaries. Yet, if he had, it is unlikely that he would have deliberately concealed such information. It does not ring true to his character, and would also have been risky. Questions of priority were strongly contested, and Tyndall tended to champion underdogs. He created considerable opposition in Scotland by advocating Louis Rendu's priority over James Forbes in the theory of glacier motion, and Julius Robert Mayer's over James Joule for establishing the mechanical equivalent of heat.³⁸ If those Scots, or others, thought Tyndall had suppressed someone else's priority for the absorption of radiant heat by carbon dioxide and water vapour, they would have been vocal in their criticism. Yet no-one seems to have protested in Britain or Europe, or indeed in America.

Tyndall did not even mention the absorption of heat by carbon dioxide and water vapour in the initial reports of his work, with the exception of his letter to Auguste de la Rive, published in the Bibliothèque Universelle, and in that letter he did not make any connection to climate. Furthermore, if Tyndall had known Foote's results, one might have expected him to start his experiments with carbon dioxide and water vapour, as being likely to give him clear results. In the event, he initially tried dry air, oxygen, hydrogen and nitrogen. His rationale was that he wanted to start by examining what he thought were the ‘simple’ gases, which he imagined at the time were monoatomic. He was driven by a desire to understand the fundamental physics, exploring the interaction of radiation with matter, and it was sensible therefore to start with what he considered to be the ‘simple’ gases. Having tried, and failed, to show the absorption of heat by those gases, it was only with the more complex molecule of coal gas that he first succeeded in showing it. Carbon dioxide and water vapour, also more complex molecules, came later. Tyndall described how increasingly struck he was with the result from water vapour, which became the focus of his research over the next few years, and critical to meteorology. This is not the behaviour of someone who already knew the result he was expecting to obtain. He had clearly not anticipated it.

In addition, Tyndall's interest in climate change was limited. Though his experiences in the mountains had led him to think about the possible impact of solar radiation on the atmosphere, and though he was well aware of theories of a previous ice-age, climate change itself was not a major driving force for his research. He did not mention it in his 1859 paper, nor in the subsequent notes published in Continental journals, and devoted just 13 lines to it in his major 1861 paper, almost as an afterthought.³⁹ He never returned to the subject. Tyndall's primary interest was in the physics itself (using radiation to probe the nature of molecules), and particularly, over time, in the role of water vapour in meteorology. It is we, not himself, who claim Tyndall as a founder of climate science in retrospect.

On the basis of this evidence, it is unlikely that Tyndall was either aware of, or had read, Foote's paper.

Conclusion

This episode raises particular questions about, and throws light on, simultaneous discovery, the nature of networks between American and European physicists in the 1850s, the significance of gender and amateur status, and the reputation of American physics and physicists in Europe.

During a period of a few years at the end of the 1850s, several people, as far apart as New York, London and Berlin, were exploring the possible interaction of radiant heat with gases. This situation of ‘simultaneous discovery’ is not uncommon in the history of science. Examples include Charles Darwin and Alfred Russel Wallace for evolution by natural selection and, closer to the subject of this paper, Mayer, Joule, Colding, Helmholtz and others for the conservation of energy.⁴⁰ Foote, Tyndall, Magnus and Rudolf Franz (following the earlier work of people such as Melloni, Saussure, Fourier, Pouillet and Hopkins) were all engaged with work on the action of heat on gases over a similar timescale. Tyndall referenced Franz's work, who had published in 1855,⁴¹ while rightly criticizing his methodology and results in his 1861 paper and in detailed correspondence with Stokes while his paper was being refereed.⁴² It was the only related work of which he was aware. He did not know of Magnus's work until 1861 (nor was Magnus aware of his, despite its extensive publication in Europe), and does not seem to have noticed Foote's work at all. The fact that Tyndall and Magnus, both leading physicists of the day and good friends, did not know of each other's work for nearly two years is indicative of a very different pattern of scientific communication from today.

Few people in America in the 1850s were active scientific researchers with the degree of expertise of those trained in the UK and Europe. Of those, only a small proportion were active in physics. Even in the 1870s, no more than 75 people in America called themselves physicists, and none beyond Benjamin Franklin and Joseph Henry had made a significant international reputation.⁴³ There was no academic community in America recognized in Europe, and indeed the concept of a coherent national community of scientific researchers in America was just beginning. What we now term physics was a particularly weak area, with the exception of astronomy and some aspects of geophysics. Natural history flourished, alongside elements of geophysics, as Americans explored and measured their country, but natural philosophy lagged behind.⁴⁴ Overall, applied research was emphasized at the expense of basic research, making work like Tyndall's the exception rather than the rule. National institutions were slow to develop, and local bodies were of greater significance, such as the American Philosophical Society in Philadelphia (founded in 1743) and the American Academy of Arts and Sciences in Boston (founded in 1780). The Smithsonian Institution had been founded in 1846, with Henry as its first director, and the AAAS in 1848 (as the renamed Association of American Geologists and Naturalists, itself founded in 1843), but the National Academy of Sciences was not established until 1863. From his position at the Smithsonian, Henry sought to encourage original research in America during the 1850s, but without the financial support necessary to coordinate activities nationally.

Direct communication about science across the Atlantic was sparse in the 1850s, and, as the institutions themselves carried relatively little weight in Europe, personal relationships were particularly important. Transatlantic travel was relatively infrequent, so written correspondence and the exchange of journals was critical. Henry had visited Europe in 1837, but not since. Tyndall himself did not yet have American contacts. Michael Faraday, Tyndall's friend and mentor, communicated at times with a number of the leading American men of science, including Joseph Henry, Benjamin Silliman, Alexander Dallas Bache and Robert Hare. Yet between 1855 and 1860 there is only one extant letter between Faraday and any of these people. This letter, from Faraday to Silliman in March 1860, responds to a request from Silliman to receive back copies of the Philosophical Transactions from 1850.⁴⁵ The implication here is that copies of this key journal were not even readily available at Yale, where Silliman was based.

Eunice Foote was disadvantaged not only by this lack of an academic community in America and poor communication with Europe, but by two further factors: her gender and her amateur status. On introducing her paper at the AAAS, according to the New York Daily Tribune, Henry commented that ‘the sphere of woman embraces not only the beautiful and the useful, but the true’,⁴⁶ and described his admiration for the well-known mathematician and scientific author Mary Somerville. At the end, he reportedly made some ‘gallant remarks in regard to the ladies’.⁴⁷ He was making the case for female participation in scientific research, but against the background of a resistant social culture that would have been equally recognizable in Britain.⁴⁸ Tyndall viewed women as having a lesser ability than men in creative scientific research, though he was also an admirer of Mary Somerville and often asked the wives of his scientific colleagues to read and comment on his writing. It is possible, if he did spot the paper in the American Journal of Science and Arts, that he skimmed straight over it when he saw the author's name, but we can only speculate. The Scientific American article, by contrast, which Tyndall is unlikely to have read, was particularly supportive of female capability, arguing that ‘Owing to the nature of woman's duties, few of them have had the leisure or the opportunities to pursue science experimentally, but those of them who have had the taste and the opportunity to do so, have shown as much power and ability to investigate and observe correctly as men’.⁴⁹ Yet this opportunity for women was a rarity. Most scientific societies excluded women on principle, on both sides of the Atlantic. Women like Maria Mitchell (1818–1889), the astronomer, were the exception rather than the rule. She was the first woman to be elected to the AAAS, in 1850, having also been the first woman elected to the American Academy of Arts and Sciences in 1848 (despite protests from the botanist Asa Gray). For her extensive comparison of American and British women scientists from 1800 to 1900, Mary Creese examined their scientific publications, as registered in the Royal Society's Catalogue of Scientific Papers, 1800–1900.⁵⁰ Globally, fewer than 1000 women authors produced some 3400 papers (of which 1400 were by Americans), less than 1% of the total published, and most of those women were active only in the last two decades of the century. The majority of papers published by American women were in botany, zoology and other biological sciences; 12% of papers were in the field of astronomy, but very few were in physics. Creese lists just 16 papers by American women in physics over the whole century. Only two pre-date 1889, and they are the two papers by Eunice Foote described above. Few women were members of the AAAS (after Maria Mitchell, only two other women were elected before the Civil War), and with the added lack of infrastructure for research in physics, largely an amateur activity in the USA at the time, Foote could hardly have done more. Even in the 1870s, when Tyndall made a highly successful lecture tour of America, a newspaper could make sarcastic remarks about the presence of women at the lectures: ‘the instructed are satisfied with what he says, and pleased with his workmanlike way of saying it, while to the young ladies he gives gorgeous exhibitions of color, which they freely admit to be most lovely, most splendid and most nice’.⁵¹

Foote's findings should have been recognized and interpreted in Britain and Europe. Henry perhaps bears some responsibility for the fact that they were not. He was the one person who could have promoted her work, but he stated that he was unable to interpret its significance. Tyndall had a clear theoretical rationale for pursuing and interpreting his experiments on radiant heat, in terms of the interaction of atoms and molecules with radiation. Foote did not give clear reasons, or reference other people. That her findings were not recognized, primitive though they were, says much about the state and reputation of American physics in the 1850s and 1860s, and her gender.

Footnotes