Who knew what about Eunice Foote’s 1856 discovery of the absorption of heat by carbon dioxide and water vapour?

UPDATE 13 February 2019: my paper giving a more extensive and updated analysis of this episode has just been published online by the Royal Society's Notes and Records, as Eunice Foote, John Tyndall and a question of priority. It is not open access, but if you would like a pdf , please email me as on my contact page.

The Irish scientist John Tyndall is often credited with the discovery of the absorption of heat by carbon dioxide and water vapour in 1859, underpinning our current understanding of the greenhouse effect, global warming, and meteorology.

Yet it has become evident in recent years that an American woman, Eunice Foote, made the discovery before him in 1856. Her results were announced at the 1856 meeting of the American Association for the Advancement of Science, and published in the American Journal of Science and Arts that year as ‘Circumstances Affecting the Heat of the Sun’s Rays’. Not only did she demonstrate the absorption of solar heat by carbon dioxide and water vapour (or, at least, the radiative absorption of energy from sunlight, as described below), but she also made the direct connection to their variability as a possible cause of climate change. Her paper was actually presented by Joseph Henry (founding director of the Smithsonian Institution). As Katharine Hayhoe reported on Twitter, following information provided by the AAAS, it was not unusual for papers to be presented by proxy at the time, regardless of gender. Eunice was not a member of AAAS but was eligible to share the privileges of membership after her husband, Elisha, became a member. And indeed Eunice did present her own paper (on a different topic) the next year.

But this all raises some significant questions. Did Tyndall know of her results, and not acknowledge them? Indeed, did anyone else in Britain and Europe note the importance of her findings? And if not, why not?

A symposium was convened at the University of California Santa Barbara, on 17 May 2018, to explore her discovery. As Tyndall’s biographer, I sent in my views, and what follows is a summary, taking into account what I understand of what was discussed at the symposium.

First, we should just note the basis of Foote’s experiment. Her experimental arrangement 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, though the specific result with carbon dioxide and moist air was not. That is Foote’s unique contribution. If Tyndall, or others, knew this, they should have cited it. However, her apparatus does not differentiate between the direct effect of solar radiation and that of re-radiated longwave infra-red. Tyndall’s apparatus only uses longwave infra-red (from a Leslie cube at 100oC), and therefore directly establishes the physical basis of what we now call the greenhouse effect. As Katharine Hayhoe and Eli Rabett have pointed out, Foote’s could not do that.

Nevertheless, 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.

There was indeed some recognition of her findings in America soon after the presentation. John Perlin, who has explored her work in detail, has identified reports in a number of places, including the New York Herald, the Canadian Journal of Industry, Science and Art, and Scientific American. 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.

But John Perlin has discovered two short summaries of her 1856 paper in Britain and Europe: in the Edinburgh New Philosophical Journal for 1857, and in the Jahresbericht for 1856 (also published in 1857). No republications of the paper itself have yet been found in British or European journals.

In addition, Perlin has noticed that an 1856 paper of Elisha Foote’s (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. Whoever selected it presumably noticed Eunice’s paper which starts on the facing page to the end of Elisha’s, but did not select it. We also know that an 1857 paper by Eunice was published in the Philosophical Magazine in 1858. However, that paper is about electrical excitation, not solar heat. It’s 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.

So, what is going on? Why does there seem to be no mention or discussion of Foote’s paper in Britain and Europe beyond those two short summaries?

I can imagine four possible reasons, not all mutually exclusive, as to why Foote’s discovery of the absorption of heat by carbon dioxide and water vapour in 1856, and her climate change suggestions, do not seem to have been properly acknowledged by anyone at the time.

1. No one strongly interested in the absorption of heat by gases noticed Foote’s paper. This is possible, even if it seems unlikely. The American Journal of Science and Arts was taken at the Royal Institution and elsewhere in Britain and Europe. Presumably at least some people saw the paper. Yet the two people who summarised it seem to have missed its significance.

The 8-line summary of Elisha and Eunice’s 1856 papers, which appeared in the Edinburgh New Philosophical Journal for 1857, reads as follows:

‘On the Heat of the Sun’s Rays. By Elisha Foote. Read by Professor Henry: These papers described experiments from which it was inferred, that the heating power of the sun’s rays varies with the temperature of the place into which the rays fall, that the temperature of air is raised by sunshine passing through it, that in the same condition rarefied air is less heated than that which is condensed, moist air more than dry air, carbonic acid gas more than atmospheric air, and oxygen more than hydrogen gas’.

It describes Eunice’s results with moist air and carbon dioxide, while attributing them to Elisha, but omits her direct conclusions about the atmosphere and climate.

In addition, a report in the New York Daily Tribune states that Elisha read his own paper, while Eunice’s was read by Henry.

The other 8-line summary of Eunice’s 1856 results, which appeared in German in the Jahresbericht for 1856 (published in 1857), reads as follows:

‘Eunice Foote hat gefunden, dass der Unterschied im Stande eines von der Sonne bestrahlten und eines beschatterten Thermometers in verdichter Luft grösser ist, als in verdünnter, in feuchter Luft grösser, als in trockener. Unter denselbem Umständen, unter welchen ein Thermometer in atmosphärischer Luft auf 41o,1, stieg, zeigte dasselbe, wenn es von Wasserstoffgas umgeben war, 40o, in Sauerstoffgas 42o,2, in Kohlensäure 51 o,7’.

It too 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 both Scottish/British and German physicists (including, possibly, Tyndall).

(Paragraph added 24 June 2018) Intriguingly, the significance of the results may also have been missed by Henry himself. He is reported in the New York Daily Tribune to have said ‘...that although the experiments were interesting and valuable, there were [many] [difficulties] encompassing [any] attempt to interpret their significance’. That might help explain why no-one actively took up the findings, and why Henry himself didn’t, as far as we know, particularly promote them anywhere.

Nor do we know exactly who would have read the summaries, or the original papers. We know, for example, that the well-connected Gustav Magnus, who was himself carrying out experiments like Tyndall’s (and later strongly challenged Tyndall on the absorption of heat by water vapour), had not heard of Tyndall’s initial results 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). It would seem that he had also not registered the report in the Jahresbericht. We have the correspondence between Magnus and Tyndall about their experiments, which contains no mention of Foote.

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.

2. Only Tyndall noticed Foote’s paper, and suppressed or ‘stole’ it. This seems unlikely on the basis that other people, as well as perhaps him, had seen the paper, and that it was summarised in at least two places. It doesn’t fit with his character, and would also have been extremely risky. Questions of priority were strongly contested, and Tyndall championed underdogs. He created considerable opposition in Scotland by advocating Louis Rendu’s priority over James Forbes in the theory of glacier motion, and Julius Mayer’s over James Joule for establishing the mechanical equivalent of heat. 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 gleefully vocal in their criticism. Yet no one seems to have protested in Britain or Europe. Did anyone protest in America?

3. Tyndall, and others, noticed the paper in passing, but dismissed it because Foote was a woman. That’s certainly a possible factor. But, though Tyndall, and many other scientists, did not believe that women had the same creative scientific capacities as men, it seems insufficient grounds to have rejected the paper entirely, especially as the bare results (though not the key conclusions) were summarised in at least two journals, in Scotland and Germany. As Spencer Weart has pointed out to me, it’s possible that her amateur status and situation in America, a ‘developing country’ outside the mainstream, were equally factors that could have biased people against a proper reading.

4. Tyndall, and others, read (or at least glanced at) the paper, but considered it did not add anything significantly new. That is possible, not least given the similarity of Foote’s approach to Saussure’s. The brief, mundane summaries in the Edinburgh New Philosophical Journal and the Jahresbericht do not give any significance to her paper. And they both miss its crucial conclusions about climate.

We should note that Tyndall himself was barely interested in climate change. It was not the driving force for his research. He did not mention it in his 1859 paper, and devoted just 13 lines to it on pages 28 to 29 in his major 1861 paper, almost as an afterthought. He never returned to the subject. His interest was in the physics itself (using radiation to probe the nature of molecules), and particularly in the role of water vapour in meteorology. It is us who claim Tyndall as a founder of climate science, not him. We should not project our current interests and priorities onto his research agenda.

Furthermore, if Tyndall had known Foote’s results, one might have expected him to start his experiments with carbon dioxide and water vapour. In fact, he initially tried dry air, oxygen, hydrogen, and nitrogen. He started by examining what he thought were the ‘simple’ gases (indeed, he thought at the time that they were monoatomic). His driving force was the physics of the process, exploring the interaction of radiation with matter, and he started with the ‘simple’ gases in consequence. It was only with the more complex molecule of coal gas that he first succeeded in showing the absorption of heat. 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. This is not the behaviour of someone who already knew the result he was expecting to obtain. He had clearly not anticipated it.

So, in summary, it is possible that Tyndall knew of the paper. But it is also possible that he didn’t. If he did know, then, just like the two scientists who summarised it for the Edinburgh New Philosophical Journal and the Jahresbericht, he may have missed its significance. That may be a function of its authorship by an amateur woman in America. But to claim that he knowingly appropriated her work would need harder evidence. No extant letters to or from Tyndall mention it (nor his private journals), including none of the 40 or so letters exchanged between him and Joseph Henry, who gave Foote’s paper (though it seems they did not correspond until the 1870s). No letters involving British or European scientists mention it that I know of. Finding such mentions might change the picture. The fact that they are lacking at the moment, is additional evidence that those who saw Foote’s paper, or its summary, simply missed the paper’s importance.

We need to know more about how much American science was actively read, and considered significant, in Britain and Europe during this period. Certainly some American papers were summarised or republished in Britain and Europe. Tyndall’s work was published in America, to the extent that, as John Perlin has found, a paper of his on colour blindness was reprinted in the 1856 journal in which Foote's paper appeared, not necessarily with his knowledge.

It seems to me that, in a not uncommon pattern (e.g. as for the conservation of energy), several people in different places were exploring this idea around the same time, including Foote, Tyndall, Magnus, and Franz (following the earlier work of Melloni, not to mention Saussure, Fourier, Pouillet, and Hopkins). Tyndall criticised Franz's work (rightly) in his 1861 paper, and had a long-running dispute with Magnus (who went to his grave in 1870 still thinking, incorrectly, that he was right). Who exactly knew what and when about the others’ work remains unclear in some respects.

On the balance of the evidence to date, I suspect that Tyndall had not read Foote’s paper, and probably didn’t even know about it.

If further evidence comes to light, I should be fascinated to hear about it.