Origins of the CO2 Theory - Four Revolutions in the Earth Sciences - page 199

fortune in the time of Napoleon and the Revolution. Fourier's fate rode the waves
of French politics, from the birth and aftermath of the Revolution; through Na-
poleon's ascension, fall, and Hundred-Day return; to the Restoration of the Bour-
bons. He was in turn “a teacher; a secret policeman; a political prisoner; governor
of Egypt; prefect of Isère and Rhône; friend of Napoleon; and secretary of the
Académie des Sciences.” 4
Fourier's major work was Théorie analytique de la chaleur ( The Analytic The-
ory of Heat ), an encyclopedic analysis of the movement of heat through fluids and
solids. Published in 1822, it quickly became a classic. 5 In Fourier's day, though
scientists did not understand the nature of heat, they had made the commonsense
observations that heat flows more easily through some materials than others, that
a hot object cools over time, and that some substances cool more slowly than oth-
ers. 6 Fourier realized that he could treat heat as a fluid, following a gradient of
temperature from a hotter region toward a cooler one. To analyze the flow, Fourier
had to invent a new mathematics that decomposes a periodic signal into a set of
sines and cosines: the Fourier series.
Yet, Fourier noted, mathematics could only go so far in studying “how far the
atmosphere influences the mean temperature of the globe,” adding, “it is to the
celebrated traveler, M. de Saussure, that we are indebted for a capital experi-
ment, which appears to throw some light on this question.” 7 Horace de Saussure
(1740-1799) was a Genevan aristocrat, scientist, and Alpine traveler. His Voyages
dans les Alpes , published as a series between 1779 and 1796, covered botany, geo-
logy, and meteorology and became one of the most popular topics of its age. 8
In 1681, a century before Saussure, the French physicist Edme Mariotte (c.
1620-1684) had written: “Although the Sun's light and heat easily passed through
glass and other transparent materials, heat from other sources [ chaleur de feu ]
did not.” 9 Building on Marriote's observation, in 1767 Saussure constructed what
today we call a solar oven: as Fourier described it, a box “covered with one or
more plates of glass, very transparent, and placed at some distance one above the
other.” 10 After the hotbox had sat in the Sun, the space below the glass reached a
temperature higher than the boiling point of water. Saussure carried the device to
4,800feetonMt.Cramont,wheretheoutsidetemperature was6°.Thetemperature
below the glass climbed to 43°. The next day, he descended nearly a mile to the
plains and repeated the experiment. At 25°, the outside air was now much warmer
thanatthesummit,butthetemperature atthebottomoftheboxwasnearlyidentic-
al tothat measured atop the mountain. Saussure concluded that the Sunshines with
nearly equal intensity at different heights but that at higher elevations the atmo-
sphere is more transparent, allowing more heat to escape.