Something's a-Foote with Climate Science History

John Tyndall, Eunice Foote, and the greenhouse effect
01 March 2020
By Jeff Hecht
Tyndall's radiant heat measurement system, with Leslie cube at the left and differential spectrometer at the right.
Tyndall's radiant heat measurement system, with Leslie cube at the left and differential spectrometer at the right. Photo Credit: Royal Institution of Great Britain

John Tyndall is often credited with discovering the greenhouse effect, but the real history is more complex. In the 1820s, French mathematician Joseph Fourier calculated that sunlight alone could not keep the Earth at its present temperature. In 1856, Eunice Foote, an American scientist and inventor, experimentally showed that sunlight heated carbon dioxide and water vapor more than air, and suggested that changes in gas concentrations might explain evidence of past warm periods. Starting in 1859, Tyndall analyzed radiation transfer and heat absorption of gases, the physical basis of the greenhouse effect.

Born of well-educated protestant Irish parents around 1820, Tyndall worked as a surveyor, then moved to Britain when a railroad boom made surveying a lucrative profession. He also briefly taught, then studied physics at the University of Maxberg in Germany. In 1853, he joined the Royal Institution in London, headed by Michael Faraday.

The following year, Tyndall gave a series of lectures on heat. In one, he shone a bright light along a jet of water flowing from a tank, with total internal reflection guiding light through the arc of liquid, delighting the audience. His later description of the effect in a popular book led some to credit Tyndall with inventing light guiding that ultimately led to fiber optics. Yet Tyndall's notes reveal Faraday suggested the idea, which Swiss physicist Daniel Colladon had published in 1842 but whom Tyndall never credited.

Tyndall also never credited Eunice (Newton) Foote, born in 1819, whose father was a Connecticut farmer named Isaac Newton, no known relation to the English physicist. Educated at the Troy Female Seminary, she took science courses at what is now the Rensselaer Polytechnic Institute. She married Elisha Foote, a lawyer, judge, and inventor, and the couple settled in Seneca Falls, New York, where both of them were early signers of a pioneering statement of women's rights in 1848.

Both Footes had papers on heating by sunlight presented at the 1856 annual meeting of the American Association for the Advancement of Science, but only Elisha spoke; Eunice's paper was read by Joseph Henry, head of the Smithsonian Institution. Her paper described how the temperature of damp air and "carbonic acid" (carbon dioxide) exposed to sunlight rose much more than that of dry air. She wrote that such elevated moisture and CO2 could account for the high temperatures geologists thought the Earth had in prehistoric times. It was the first time anyone had suggested changes in the atmosphere could change climate. Her idea made Scientific American and the New York Daily Tribune. The American Journal of Science and Arts printed both her and Elisha's papers, but that success was forgotten after she went on to other things.

Eunice Foote's paper

Eunice Foote's paper, which appeared in American Journal of Science and Arts in 1856.

Tyndall began studying heat absorption in gases in the spring of 1859, and never cited either of the Footes' papers. Yet John Perlin, a visiting scholar at the University of California in Santa Barbara, believes Eunice's paper inspired Tyndall's efforts. Perlin says Tyndall should have had access to her paper because he was an editor of the British Philosophical Magazine, which reprinted Elisha's paper from the American Journal, but not Eunice's closely related shorter paper which was published in the same issue.

Support from the Royal Institution and an expertise in measurement allowed Tyndall to conduct more sophisticated experiments than the Footes could as amateur scientists and independent inventors. Whereas the Footes measured temperatures by reading thermometers in sealed glass cylinders illuminated by direct sunlight, Tyndall used "radiant heat" from a Leslie cube containing water at the boiling point-a simple blackbody source. He built a differential spectrometer to measure light absorbed by gas passing through a 30-inch tube.

Tyndall first reported heat absorption in gases to the Royal Society on 25 May 1859, followed by a 10 June talk to the Royal Institution. His written summary mentions only "coal gas," a mixture of hydrogen, methane, and other gases produced by heating coal then used for lighting and heating. He concluded, "the atmosphere admits of the entrance of the solar heat, but checks its exit, and the result is a tendency to accumulate heat at the surface of the planet." To bolster his claim to the discovery, he sent papers to three European journals as well as publishing his work in England.

Sickness and a frenetic schedule interrupted Tyndall's work on radiant heat until June 1860, when he began measuring absorption of other gases. Only on 20 November 1860, did he finally measure moist air, finding that its absorption was comparable to that of CO2, but less than coal gas. With hindsight, we can recognize the greenhouse effect in Tyndall's early data, but the "radiant heat" he was measuring included both visible and infrared light.

Not until 1864 did Tyndall begin to study the differences between visible light and the infrared, which he called "black" or "obscure" heat because it was invisible to the eye. He found solar radiation reaching the ground was mostly visible, but the "heat" radiated by the Earth and hot surface objects was largely infrared. That infrared light had up to 25 times the heating power of visible light, and could heat platinum to incandescence, an effect he called "negative fluorescence" because it converted long wavelengths into shorter ones. Physicists spent years debating its nature and its relationship to fluorescence.

We don't know exactly why Tyndall never credited Eunice Foote with inspiring his work. His attitude toward women very likely contributed. Tyndall-like many other men at the time-thought women were inferior to men and lacked their scientific originality, so he might have ignored a discovery claimed by a woman. He was also ambitious, an Irishman seeking acceptance by British scientists. He also failed to credit discoveries by men like Colladon, and quarreled over priority with some other prominent scientists of his time.

After a second paper on electrical excitation in 1857, Eunice Foote faded away from the world of physics. She was the first American woman to publish on physics (not counting astronomy), which wouldn't happen again until 1889. She may have felt unwelcome in science, or may have chosen to focus on the more practical world of invention and technology. In 1857, a court awarded Elisha Foote a small fortune for infringement of his 1842 patent on stoves. In 1860, Eunice patented a new filling that stopped shoe soles from squeaking. Later she developed an improved paper-making machine.

Others built on Tyndall's work as he had built on Eunice's. In 1896, Swedish scientist Svante Arrhenius calculated how much atmospheric carbon dioxide warmed the Earth. In 1938, English engineer and inventor Guy Callendar calculated that the increase in CO2 levels over the previous 50 years was enough to explain the rise in global temperatures. Many others who followed them stood on their shoulders to build modern climate science.

Jeff Hecht is an SPIE Member and freelancer who writes about science and technology.

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