The Summer She Put in a Jar

In 1856, Eunice Newton Foote put two glass cylinders in the sun and watched one of them become hotter than the other. The cylinders were each about four inches across and thirty inches long. Inside each one sat a pair of thermometers. With an air pump, she could remove air from one cylinder, compress it into the other, dry it, moisten it, or replace it with another gas.

The most interesting gas was what she called “carbonic acid.” We call it carbon dioxide. In ordinary air, her thermometer reached 106 degrees Fahrenheit. In carbon dioxide, it reached 125. The tube containing the gas also took much longer to cool after it had been taken out of the sunlight.

Foote did not have the language of modern climate science, but she had the important thought. “An atmosphere of that gas would give to our earth a high temperature,” she wrote. She had made a small, imperfect model of a large planet, and then understood what the model implied.

A laboratory made of household things

Foote was not working in a great observatory or a government laboratory. She had been educated at Troy Female Seminary, where students could take practical science classes at the nearby Rensselaer School. She later lived in Seneca Falls, New York, with her husband, the patent lawyer Elisha Foote. She was also a signatory of the Declaration of Sentiments at the 1848 convention for women’s rights.

Her experiment was simple enough to describe and difficult enough to get wrong. The two cylinders had to begin at the same temperature. The thermometers had to be read repeatedly as the vessels sat in sunlight or shade. The air in one could be rarefied while the other was condensed. For moisture tests, one sample was dried with calcium chloride and the other saturated with water vapour. She compared common air, hydrogen, oxygen and carbon dioxide.

The pattern was not merely that a dark object gets hot in the sun. The gases behaved differently. Moist air warmed more than dry air. Condensed air warmed more than rarefied air. Carbon dioxide produced the largest reading of all. Foote also noticed that the carbon-dioxide vessel stayed hot after removal from the sun, a result she described as “many times as long in cooling.”

Her measurements were not a modern controlled experiment. She could not state the pressure of the gases precisely, and her glass cylinders did not allow her to separate every possible source of heat. The paper does not identify the glass in enough detail to settle how much of the radiation it transmitted. Still, the observation was clear enough to lead her beyond the apparatus. If Earth’s air had once contained a larger proportion of carbon dioxide, she reasoned, its temperature would have been higher.

That was an astonishing conclusion to draw from four thermometers and a pump.

The paper was present, but she was not

In August 1856, Foote’s paper was presented at the annual meeting of the American Association for the Advancement of Science in Albany. Foote did not read it herself. Joseph Henry, the first secretary of the Smithsonian Institution, read it for her. Her husband, Elisha, presented his own paper at the same meeting.

Henry introduced her work with a sentence that has survived: “Science was of no country and of no sex.” It was meant as praise, but it also marked the boundary she had crossed. Foote did not occupy the ordinary role of the person explaining her own results to the room.

The paper was not included in the association’s published proceedings. It did appear in full in the American Journal of Science and Arts later that year, occupying only two pages. A brief notice in Scientific American praised the experiments, pointedly noting that “this we are happy to say has been done by a lady.” Then Foote’s work disappeared from the working history of the subject.

The disappearance is easy to turn into a neat story about sexism, and sexism certainly shaped the institutions around her. But the record is less theatrical than a theft. There is no evidence that John Tyndall, whose work became foundational, had read Foote’s paper. There is no evidence that he copied her. The more uncomfortable explanation is that a result can be printed and still fail to enter the conversation, especially when the author is outside the profession and the measurement does not fit the instruments that later become standard.

What Foote found, and what Tyndall proved

Three years after Foote’s experiment, John Tyndall began studying the transmission of radiant heat with a much more elaborate apparatus. He sent heat through a tube, used a thermo-electric pile to detect it, and compared gases one by one. His 1859 paper showed that gases differ greatly in how they absorb radiant heat. He went on to identify the physical process that makes the atmosphere warm: sunlight enters relatively easily, while heat radiated from the warmed Earth is absorbed on its way out.

This distinction matters. Foote demonstrated that carbon dioxide and moist air became hotter in her sunlit vessels, and she correctly connected changing atmospheric composition with climate. Tyndall measured the absorption of long-wave infrared radiation, the form of heat emitted by Earth’s surface. Foote’s cylinders could not cleanly distinguish direct solar heating from infrared heat re-radiated inside the vessel. She found an important effect without fully identifying its mechanism.

Priority, then, depends on the verb. Foote was earlier in showing that changing the gas could change the temperature and in proposing a climate consequence. Tyndall was later in establishing the radiative physics of the greenhouse effect with an instrument designed to isolate it. Calling only one of them the discoverer makes the history flatter than the experiments were.

The older history is longer still. Joseph Fourier had proposed in 1824 that the atmosphere could raise Earth’s temperature, and Claude Pouillet developed related ideas in the 1830s. Foote did not invent the notion that an atmosphere affects climate. She supplied a compact experimental link between a particular gas and that planetary idea. Tyndall supplied a deeper physical account. Modern climate science needed both kinds of knowledge.

The lost page comes back

For more than a century, Foote’s experiment remained an obscure item in an old journal. In 2011, Raymond Sorenson, a retired petroleum geologist and collector of historical science books, found a summary of it in an annual review of scientific discoveries. He traced the reference back to the original paper and published an account of her priority.

The rediscovery did not make Foote the secret inventor of all climate science. It corrected the shape of the beginning. The familiar story had treated the greenhouse effect as a road running from Fourier to Tyndall, with no one in between holding a pair of glass tubes in the sun. Foote’s experiment inserts a person, an apparatus and a result into that empty space.

Her work is valuable partly because it is unfinished. The tubes did not reproduce the atmosphere. The readings were rough. The mechanism was not yet clear. But science often advances through observations that know more than their instruments can explain. Foote saw that air was not just empty space between the Sun and the ground. It could change what happened to heat.

A century and a half later, the atmosphere is still being treated as an experiment, only now the cylinders are the size of a planet and the thermometer does not belong to one investigator. The small glass vessels have vanished. Their question has not.