Eunice Foote

"Circumstances affecting the heat of the sun's rays" (1856)

Eunice Newton Foote (1819–1888) was an American scientist and women's rights campaigner. In 1856, she published a paper in The American Journal of Science and Arts documenting her experiment showing that carbon dioxide is a greenhouse gas. This is several years before John Tyndall made the same discovery at the Royal Institution of Great Britain.

Here are some key passages from her paper, "Circumstances Affecting the Heat of the Sun's Rays":

"The experiments were made with an air-pump and two cylindrical receivers of the same size, about four inches in diameter and third in length. In each were placed two thermometers. . . ."

After various experiments looking at the effect of filling the cylinders with high-pressure air, low-pressure air, humid air, and dry air, Foote filled one cylinder with carbon dioxide and the other with regular air. She placed each cylinder in the sun and watched the thermometers.

"The highest effect of the sun's rays I have found to be in carbonic acid gas [i.e., carbon dioxide*].

"One of the receivers was filled with it, the other with common air, and the result was as follows . . . . The receiver containing the gas became itself much heated—very sensibly more so than the other—and on being removed, it was many times as long in cooling. . . . On comparing the sun's heat in different gases, I found it to be in hydrogen gas, 104º [Fahrenheit]; in common air, 106º; in oxygen gas, 108º; and in carbonic acid gas, 125º."

Foote recognized what her discovery meant for carbon dioxide's power to affect the climate:

"An atmosphere of that gas [i.e., carbon dioxide] would give to our earth a high temperature; and if as some suppose, at one period of its history the air had mixed with it a larger proportion than as present, an increased temperature from its own action as well as from increased weight must have necessarily resulted."

You can download the full paper as a PDF or see it in the original journal from the Internet Archive. You can cite the paper as:

Eunice Foote, "Circumstances Affecting the Heat of the Sun's Rays," The American Journal of Science and Arts 22, no. 66 (November 1856): 382–383.

* At the time, carbon dioxide (CO₂) was often referred to as "carbonic acid gas." So, even though chemists today use the term 'carbonic acid' to refer to a different chemical compound (H₂CO₃), Foote uses 'carbonic acid gas' as a name for carbon dioxide.