The Trailblazing Work of Eunice Foote - Part I
Scientist, inventor and women's rights advocate (1819-1888)
In Circumstances Affecting the Heat of the Sun’s Rays (1856), Eunice Newton Foote offered a groundbreaking hypothesis: higher concentrations of carbon dioxide in the atmosphere could have caused warmer climates in Earth’s distant past1. The importance of Foote’s experiments gained some recognition immediately but then fell into obscurity. Foote kept a place in history for her role in the first convention on women’s rights in Seneca Falls in 18482. From the 1970s, she was again recognised as a trailblazing scientist, including with a short biography in a self-published textbook by Elizabeth Wagner Reed3 in 1992. However, it wasn’t until 2011 that Foote was rediscovered to the public with the publication of an article highlighting her experiments in the context of an early contribution to climate science4.
Several other illuminating commentaries have followed, but much remains a mystery. Contrary to some popular headlines5, and as has been noted, Foote's experiments did not directly probe the greenhouse effect that underlies global warming6. Nonetheless, this two-part article will explain how her experiments achieved a place in the vanguard of a broad and radical advance in physics. In Part I, we’ll climb to the best vantage point by examining the preceding ideas of the Renaissance, Enlightenment and Industrial Revolution. Part II will explore the details of Eunice Foote’s investigations and offer an illuminating comparison to the earlier work of Joseph Fourier and the later works of John Tyndall and Josef Stefan.
Three preceding revolutions
Let’s imagine a giant is drinking from Lake Como through different length pipes — when the pipe is eleven metres high in the sky, no matter how strongly the giant sucks in the air, the water won’t reach his mouth. From a height of nine metres it is fine to drink, but eleven is impossible. Why? Luckily, it’s 1643, and a day’s stroll away in Florence, Evangelista Toricelli7 (1608-1647) has just had an epiphany:
1.Air has weight “Noi viviamo sommersi nel fondo d'un pelago d'aria.” We live submerged at the bottom of an ocean of air. Toricelli,1642
He explains to the giant his astonishing discovery: the weight of the atmosphere above us is equivalent to that of a 10-metre column of water. This atmospheric pressure pushes down on the lake while the water in the pipe is protected from the downward pressure by the partial vacuum formed when the air is sucked out. The water surges up to a maximum height of ten metres to restore balance.
Toricelli invented the mercury barometer to solve the enigma, and it has become a household item because changes in atmospheric pressure can often signal approaching storms. Mercury, thirteen times denser than water, rises to the more manageable height of 76 centimetres below a vacuum (see Figure 2). So, Aristotle’s ideas, such as the four elements of Earth, Fire, Water and weightless Air, were now being challenged by Gallileo, Toricelli and other Renaissance thinkers. But what exactly is this mysterious "air"?
Robert Boyle (1627-1691), who had a formative influence on Isaac Newton and was also his friend8, kickstarted the second revolution, rejecting Aristotle’s elements and setting out an early modern notion of chemical elements in his treatise The Sceptical Chymist 1661: “Elements… are the Ingredients of all those call'd perfectly mixt Bodies are immediately compounded, and into which they are ultimately resolved”. Later, the experiments of Joseph Black (1728-1799) (re)discovered9 carbon dioxide (“fixed air”), showed it was present in the atmosphere and quantified its higher density relative to the air (at the same pressure):
2.Air can be of different compositions with varying effects “I mixed together some chalk and vitriolic acid… The strong effervescence produced [CO2] an air or vapour, which, flowing out at the top of the glass, extinguished a candle that stood close to it; and a piece of burning paper immersed in it, was put out as effectually as if it had been dipped in water” Black,1750
Carbon dioxide's distinguishing characteristic, compared to common air, was its ability to extinguish flames — a property still valued today for putting out electrical fires (see Figure 2). Oxygen and nitrogen were also isolated and studied in detail over the following decades. Just before Foote's experiments, John Dalton (1766–1844) proposed an early atomic model of CO2, visualising it as a carbon atom flanked by two oxygen atoms. However, the periodic table wouldn’t emerge until 1869, and the debate over whether matter was continuous or composed of discrete atoms had no decisive contributions until Einstein’s work in 1905.
The final revolution takes our attention from air to light in anticipation of Eunice Foote linking the two.
In 1748, Emilie du Chatalet, fearing that she would not survive bearing her fourth child at the age of forty-two, worked day and night to complete what would become an important work of the Enlightenment Era. Du Chatelet was translating Isaac Newton's famous Principia into French, with her corrections and additions comprising two-thirds of the volume. Du Chatelet died a week after giving birth, and her friend, the Mathematician Alexis Claude Clairaut, published her book posthumously ten years later. Still the standard French translation today, it included the first rigorous derivation of conservation of total energy from the principles of mechanics, for which Du Chatelet should be recognised in every mechanics textbook!
Emilie Du Chatalet’s (1706-1749) own magnum opus was the Institutions de Physique, but it is her entry into the Academy Prize10 competition, DISSERTATION ON THE NATURE AND PROPAGATION OF FIRE, that brings her into our story for prefiguring the discovery of infrared light:
I.“If the Sun Were a Globe of Fire it Could Not be the Center of Our Planetary World.”*
II.“A very curious experiment would be to separately gather enough homogeneous rays to test whether the primary rays that produce the sensation of different colours in us might also have different burning properties.”
III.“…there might be in nature other colours than those we know in our world.”*
Emilie du Chatelet,1737 *Translated by Isabelle Bour
Her essay is a fascinating window into Enlightenment thought, full of brilliant reasoning and entertaining experiments. (I) argues that the Sun must be a weighty body of substance to hold together the solar system by gravity and generate the (roughly weightless) fire that illuminates us continuously. Though tangential to this exploration, the quote reveals the dizzying scope of Du Chatelet’s philosophy and opportunes the mention that it was another woman—Cecilia Payne Gaposchkin—who, two centuries later, deduced that this material body is mostly composed of hydrogen. From context elsewhere in the essay, it is clear that the homogeneous rays of (II) are formed by refraction through a prism. And thus —the finale— if one were to look for burning via homogenous rays beyond the primary red colour, then one might find an unknown `colour’(III), such as infrared.
Figure 2 shows a NASA/JPL-Caltech educational reproduction11 of the 1800 experiment William Herschel conducted at the age of sixty-two. It was in the vein of Du Chatelet’s “expérience bien curieuse”12, written conicidentally within a year of Herschel’s birth. On a sunny winter’s day in Slough13, perhaps accompanied by his sister Caroline, William Herschel (1738-1822) used a prism to disperse the sun’s rays into its constituent colours onto a row of thermometers. Not only did he find that the different colours of sunlight produced “different burning properties”, but that beyond where light of the visible colours fell, some “unknown” rays were being registered through a reading on the furthest thermometer:
3.Unified light and (radiant) heat “I likewise conclude that the full red falls still short of the maximum of heat; which perhaps lies even a little beyond visible refraction. In this case, radiant heat will at least partly, if not chiefly, consist, if I may be permitted the expression, of invisible light; that is to say, of rays coming from the sun, that have such a momentum14 as to be unfit for vision.” Herschel,1800
In fact, the sun’s spectrum peaks in the green portion of visible light, but atmospheric scattering can shift the peak into the red for an observer at ground level. “Invisible light”! - the contradiction illustrates how science can lead one to surprising and counterintuitive places that become part of common sense: think of bats seeing in ultraviolet and the use of thermal cameras to see in infrared. William Herschel’s son, John, made the first thermal image, calling it a “thermogram” in 1840. Then, the first device to measure infrared was the bolometer developed by our old friend Samuel Langley in 1878 (see climatephysics’s first article). This distinction between sunlight’s visible and invisible parts, which developed throughout the 19th Century, will be crucial in understanding the scope of Eunice Foote’s experiments.
Having rewound the clock,
we will now be ready to step into Eunice Foote’s lab and understand some of her aims and achievements. As a taster of what’s to come, we wrap up Part I with a fascinating example of the reception of her work15
“It is believed and taught by geologists that during [the Devonian] the period preceding the carboniferous era,—when the coal bed materials were forming—that the atmosphere of the earth contained immense quantities of carbonic acid [CO2], and that there was a very elevated temperature of atmosphere in existence, in comparison with that of the present day.Those who believe that this earth was once a fiery ball, attribute this ancient great atmospheric heat to the elevated temperature of the earth; but Mrs. Foot’s [sic] experiments attribute it to a more rational cause, and leave the Plutonists but a small foundation to stand upon for their theory.” Scientific ladies–experiments with condensed gases’, Scientific American (12, 5, 1856).
see you in 2025 for Part II.
— Richard and the Climate Physics Team
References
Flagged by Wikipedia: A 1902 news article highlighting a speech from the famous suffragist and abolitionist Susan B. Anthony, mentioning Foote, her contemporary.
Geneticist Dr Elizabeth Wagner Reed’s American Women in Science Before the Civil War (1992) is a fascinating collection of short biographies. It details Foote’s science, perhaps for the first time, but appears to have often been overlooked, perhaps partially because it was self-published. An NYT article celebrated Reed’s life.
e.g. Amara Huddleston -2019 - NOAA and Ortiz and Jackson - Notes and Records - 2022
The Dutch atomist Isaac Beeckman should also be mentioned here.
Though Black did not offer the citation, his work built on that from Jan Baptist van Helmont (1580-1644), who coined the term gas (from the Greek word for chaos) and used it to describe what is given off when burning coal (CO2).
du Chatelet refers to the work of Boyle, along with many others…
experience and experiment are the same words in French
See Herschel and Puzzle of Infrared (Amercian Scientist 2012) for reanalysis of the original data.
Herschel’s reference to momentum appears to be a prescient addition to Newton’s corpuscular theory of light. Notably, the phenomenon of radiation pressure, a logical consequence of light possessing momentum, was not proposed until James Clerk Maxwell in 1862. This has application today with “solar sails”.
Quoted in Jackson and Ortiz 2022. Cited and discussed earlier by Elizabeth Wagner Reed in Chapter “Experimenter on gases” (1992).