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Global Warming Science At The Barricades: Claude Pouillet, The Sun, And 1849

Updated on December 7, 2020

A forest of bayonets

“A forest of bayonets,” thought Claude Servais Mathias Pouillet, Professor of Physics at the Sorbonne and Director of the Conservatoire des arts et métiers, in whose courtyard this unwelcome forest now stood. The bayonets were at the back of the crowd, behind the leadership—Ledru-Rollin, Victor Considerant with his absurd moustaches, other Deputies in the full regalia of their office. It was an allegory of the state—pomp backed with steel.

Pouillet knew this as well as any; he had been representative for Poligny in the Jura mountains, not so terribly distant from Cusance, where he had been born. Then the revolution of 1848 had swept his patron, the “citizen king” Louis-Phillippe, from power into exile, and Pouillet’s duties had become exclusively academic once more.

Vernet's "Barricade, Rue Soufflot"

"The Day of the Bayonets"--June 13, 1849

It is not clear today what Pouillet knew of the larger events of “the day of the bayonets”--June 13, 1849. He must have shared in the general knowledge that Louis-Napoléon, President of the fledgling Second Republic, had sent French troops into Rome in order to help restore Papal government; and that the Left, bitterly opposed to this unconstitutional action, were mounting a massive demonstration in protest. But had he heard that General Changarnier’s cavalry had charged the marchers without so much as an order to disperse? That “the dragoons in a frenzy fell to riding down people, striking them with the flat of their swords and using the edge at the least resistance?” We can no longer be sure.

But surely Pouillet must have wondered why the Deputies and their followers had come here, to the Conservatoire. The Legislature would have been a more logical destination. Regardless of their reasons, they posed a terrible threat to the artifacts--and even the building itself. The main thing was to persuade them to leave. It would not be easy, he knew; times were difficult, and he was facing angry and frightened men with nothing more than the eloquence honed in Assembly and classroom, whatever wisdom his fifty-nine years had brought to a naturally keen mind, and an energy that still belied those years.

Main entrance, Conservatoire National des Arts et Metiers

Photo courtesy of aviewofcities.
Photo courtesy of aviewofcities.

The Dialog

Certainly his membership in the Legion of Honor would not help, nor that in the French Academy, nor would his researches into electricity, magnetism, fluid dynamics, or meteorology, nor would his distinguished teaching record—least of all, his appointment to teach physics to Louis-Phillippe’s children. His origins in the Franche-Comte region might provide some slight help--Considerant was a Comtois, too. But then, Considerant had also campaigned to take Pouillet’s place as Deputy.

“What do you want?” Pouillet asked Ledru-Rollin.

“A refuge.”

“This establishment is the refuge of science and peace, not of war. Go elsewhere with your banner.” He tried to keep any trace of bitterness from his tone.

“We are being beaten and cut down in the boulevards and the streets.”

“The Conservatoire will not save you; it will be fatal to you.”

“In the streets we will be massacred.”

“Here you will be surrounded, assailed from all sides without any means of defending yourselves.”

“Time is passing. We want a place to talk. Have you a room for us?”

He must hope time would be granted to gain some trust from these men, to persuade them that the refuge they sought was not to be found here.

“You have forced your way in. Alone against you and your army, I have only my words with which to oppose you. If you don’t believe me, if you cannot see the danger you are in here, come and I will open up a room for you.”

Thermopile by Pouillet

Pouillet the experimentalist

Pouillet’s drive to protect the Conservatoire seems understandable. It had been founded, essentially as a museum of technology, during the original Revolution, and had been evolving since the 1820’s into what we would now term a technical college. It continues as such to this day, now under the name of Conservatoire National des Arts et Metiers. Pouillet’s position as director made him directly responsible for its safety. Pouillet was also at risk personally--his Orleanist political background made him suspect in the troubled power politics of the day, even as it equipped him to accurately evaluate the threat that it posed. Beyond professional responsibility and concern for his own career, however, lay a genuine passion for experimental physics and the devices that served it.

Like Horace de Saussure before him, Pouillet was a prolific builder of instruments. For his electrical studies, which elaborated upon the now much better-known work of Georg Ohm, he had developed two types of galvanometers to measure current flow, as well as thermopiles to generate electromotive force or measure heat. There was a device to study the partial pressure of gases. And he built both a “pyrheliometer” and an “actinometer” to study heat transport within the atmosphere—or, as he conceived it, the heat contributed to the Earth by either the sun or the “heat of space.” (The latter erroneous concept he inherited from Fourier. Pouillet’s results at least showed that the “temperature of space” must be significantly lower than previously estimated, and can thus be seen as a step in the right direction.)

Using these instruments effectively required considerable diligence. Here is Pouillet’s description of the method used to make observations with the pyrheliometer:

. . .the pyrheliometer is held in the shade, but very near the place where it is to receive the sun: it is placed so that it looks towards the same extent of sky, and there, for four minutes, its warming or its cooling is noted from minute to minute; during the following minute it is placed behind a screen, and then adjusted so that on removing the screen at the end of the minute, which will be the fifth, the solar rays strike it perpendicularly. Then, during five minutes, under the action of the sun, its warming, which becomes very rapid, is observed from minute to minute, and care is taken to keep the water incessantly agitated; at the end of the fifth minute the screen is replaced, the apparatus withdrawn into its first position, and for five minutes more its cooling observed.

A long series of observations, carried out over the course of many sunny afternoons in 1837 and 1838, provided Pouillet with solid data on the solar contribution to Earth’s heat budget, enabling him to estimate what we now call the solar constant. For a first attempt, he was spectacularly successful, arriving at a value about 10% below the value accepted today. Samuel Langley, working at the turn of the twentieth century, did not do as well.

Pouillet also analyzed solar temperature and the absorptivity of the atmosphere in the same paper, his 1838 Mémoire sur la chaleur solaire, sur les pouvoirs rayonnants et absorbants de l’air atmospherique, et sur les temperatures de l’espace. (“Memoir on solar heat, the radiative effects of the atmosphere, and the temperature of space.”) These estimates do not hold up as well—he overestimated atmospheric absorptivity by a factor of two, and underestimated solar temperature by a factor of about three--though the discrepancies are not due to mistakes on Pouillet’s part, but rather to the fact that crucial pieces of relevant theory were as yet unknown in his day.

Pouillet's"signature invention," the Pyrheliometer

The Outcome

At the Conservatoire during the afternoon of June 13, not only unknowns but rampant confusion dominated the anxious scene. At first occupying the amphitheater, the demonstrators moved to the Salle des Filiatures; Ledru-Rollin appeared physically ill with worry; Considerant could not command the attention of more than a few people at a time. Emissaries were sent to seek help from political allies, but little news and no help was forthcoming. A proclamation of insurrection was at some point drafted and sent to a political journal, though no-one can say by whom, or with what authority. Considerant wrote:

“Minutes passed. Nothing happened. People conversed in groups of two, three, six; they came and went; but there was not a single general discussion, not a single decision taken in common. A few individuals shouted, “Aux armes!” asking for cartridges and for the order to build barricades. At the same time people kept running up to newcomers asking for news. People kept on waiting, but the National Guards from the demonstration did not come.”

Pouillet did not rest from his efforts to persuade the intruders to leave, focusing often on his fellow Comtois, Considerant. Just as the latter had persuaded most of his colleagues that they should go seek out the Sixth Legion of the National Guard, the regular army arrived. Shots were fired; panicked demonstrators broke windows to escape. Chaos reigned. The Deputies were told they would be shot; rifles were leveled at them but not fired. Inexplicably, the army troops suddenly left. The main gate was shut and blocked, but the remaining demonstrators found unlocked secondary doors and fled through the Conservatoire garden.

Inside CNAM today

Inside the institution Pouillet served and tried to save.  Courtesy Wikipedia commons.
Inside the institution Pouillet served and tried to save. Courtesy Wikipedia commons.

The Aftermath

For Pouillet the immediate crisis was over, and with no great damage to the Conservatoire. But it must have been not so much a relief as a re-focusing of anxiety: though a physical disaster had not occurred, what of the political realm? The event would justify such fears, as it turned out—on June 15, Pouillet was dismissed as director on the grounds that he had not opposed the occupation with sufficient vigor. It is hard to imagine what else he could have done, and easy to imagine that his Orleanist politics were the real reason for his dismissal—although it surely did not help that it was his secretary, Louis Dupin, who had helped Considerant and the others find their way out through the Conservatoire garden.

It was to be the beginning of what must surely have been the darkest period of Pouillet’s life. That same year his son died at the age of 17, and in 1850 his daughter followed at the age of 20. Perhaps he found some solace from these cruel blows in his work; for example, it was in 1850 that the last of his three important books, the Notions générales de physique et de météorologie á l’usage de la jeunesse, appeared. But that solace would soon be assailed as well.

On December 2, 1851—the 47th anniversary of Napoleon Bonaparte’s Imperial coronation-- Louis-Napoléon was finally able to seize personal control of the French state. A referendum provided political cover, and the Republic was officially ended on December 2, 1852 with Louis-Napoléon’s proclamation as Emperor Napoléon III. All government functionaries, including professors, were required to swear an oath of loyalty to him. Pouillet refused, and was dismissed from his remaining post, the physics chair at the Sorbonne.

Napoleon III

Later life

But Pouillet, if saddened, would not be crushed.  His retirement would be long and active, marked by the publications of Mémoires on topics as varied as alcohol and magnets, and by energetic participation in the affairs of the French Academy.  (Biographer Vespereau called him “one of the most active members” in 1861--Pouillet’s seventy-first year.)

He would die at last on June 14, 1868—one day after the 19th anniversary of the “day of the bayonets.”  His widow left many of his works to the municipal library of the city of Besançon, where he had come to study at the Lycée so many years before--just a papermaker’s boy from the Cusance countryside.  A street in the picturesque riverside “boucle du Doubs” quarter of Besançon bears his name today.

Claude Pouillet

Pouillet in later life
Pouillet in later life


Called a “great physicist” in his own day, Pouillet has sunk into the demi-obscurity of those who “fall just short of fame.” The Dictionary of Scientific Biography (New York, 1970-1980) sums up his work as containing “many individual advances but. . . no major innovations.” Still, his work on the solar constant must command respect as an important milestone. Perhaps one ought to say not "milestone" but "cornerstone," since accurate knowledge of solar energy input to Earth's atmosphere is a prerequisite for climate science. Still more consequential, however, was Pouillet's advancement of the work of Fourier, and its transmission to future researchers—most notably Svante Arrhenius, who cited the Mémoire sur la chalure solaire. . . in his famous 1896 paper, On the Influence of Carbonic Acid in the Air upon the Temperature of the Ground. More generally, Pouillet’s experimental prowess reminds us today that the current theory of global climate change does not rest upon mere theory only, but upon myriad observations, carried out with care, skill, and ingenuity—including a certain series made on those sunny afternoons in 1837 and 1838.

This hub is second in a series. Read the beginning of the story at "The Science Of Global Warming In The Age Of Napoleon."

Arguably the first scientific papers laying the groundwork for global warming science were the work of brilliant mathematician, and Napoleonic official, Joseph Fourier. Read about his life, work, and times.

Or, continue the story of climate change science with my Hub on global warming science in the age of Queen Victoria--John Tyndall was a great experimental physicist, educator, and--mountaineer.


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