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The Pregnant Scientist Who Raced Against Death to Transform Physics

In 1749, Emilie du Châtelet feared bearing a child at 42 would be the last thing she did. In her final year, she worked furiously on a magnum opus that would change the world.

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Illustrations by Michelle Mruk.

In the early hours of one morning in May of 1749, Gabrielle Emilie le Tonnelier de Breteuil, the Marquise du Châtelet, worked furiously at her desk in an ornate three-storied Parisian house. Piles of books on mathematics and scientific instruments littered her desktop and spilled over onto the floor, the bureau, the shelves. The marquise’s fingers were stained dark with ink, but she didn’t care. No one important was going to see her anytime soon. She had long given up the pleasures of society life.

Splayed out next to the marquise was a red, morocco-bound copy of Sir Isaac Newton’s Philosophiæ Naturalis Principia Mathematica (Mathematical Principles of Natural Philosophy), the 510-page, three-volume masterpiece that had revolutionized the scientific world and helped usher in the European Enlightenment. What had started as a basic translation from Latin into French had now morphed into a full-blown commentary. The work had proven much more difficult than anticipated, even for someone as educated and intellectual as du Châtelet. But she had come too far to give up now. This book, the first of its kind, was to be her legacy.

The marquise was exhausted. She was 42 years old and six months pregnant with her fourth child. The father was not her husband, but her much younger lover, a poet-soldier named Jean François de Saint-Lambert. Taking lovers outside of marriage was acceptable in the social circles in which du Châtelet moved, but physical evidence of them was not. Others at court had already begun talking and making jokes behind her back. But the marquise had bigger concerns than her reputation. At such an advanced age, she suspected her pregnancy would also be her end. In a time when overall life expectancy was short enough, having a child in your 40s posed considerable health risks. But she was determined to finish her commentary, to which she had devoted the last five years of her life, before she died. She had sequestered herself inside her Paris home and forced herself to work around the clock.

In one of her letters to Saint-Lambert from this period, she informed him of her daily routine. She rose at 9 a.m., sometimes 8, and worked until 3 p.m., when she allowed herself a one-hour break for coffee. At 4, she began work again, and didn’t stop until 10, when she had dinner alone. After dinner, around midnight, she started writing again, only stopping when she collapsed into bed around 5 a.m. She got three or four hours of sleep before waking up and doing it all over again the next day. Such had been her schedule for the last several months.

Her new regimen was grueling but effective, and she blamed herself for not adopting it sooner. “Had I led this life since I came to Paris, I would have finished by now,” she wrote Saint-Lambert. “But I began by having many engagements; I gave myself up to society in the evenings. I believed that the day would suffice.”

As her pregnancy continued, however, du Châtelet became increasingly aware that she was running out of time. “I felt that the only way to avoid all these intersecting inconveniences and to make the most of my trip to Paris…was to sequester myself absolutely, to stake my all, and to devote all my time to my book.”

Her commitment eventually paid off. Sometime in the first three days of September, du Châtelet finished her commentary. On September 4, she gave birth to a daughter. Six days later, du Châtelet was dead.

It was an abrupt end to an unpredictable life. The marquise never got to see her commentary published. It remained buried until 1759, when the return of Halley’s Comet to Earth’s atmosphere reignited interest in Newtonian mechanics and prompted one of du Châtelet’s mentors, Alexis-Claude Clairut, to publish it. To this day, it remains the only full translation of the Principia in French.

Perhaps most tragically, although the marquise accomplished a feat few could have, most of history has relegated her to a footnote. She has been remembered as merely the assistant to “greater” men, most notably Voltaire, France’s pre-eminent writer and philosopher, with whom she had a passionate, decade-long affair. Yet du Châtelet’s impressive body of work shows a fiercely independent and intellectual mind, one that is long overdue for its own place in history.  

* * *

In Emilie du Châtelet: Daring Genius of the Enlightenment, historian Judith P. Zinsser suggests that the idea for translating the Principia likely first came to du Châtelet in the summer of 1744. The marquise was entertaining the French Franciscan friar and mathematician Father François Jacquier at her husband’s country château in Cirey. Jacquier was a great admirer of the marquise. He and a colleague had recently completed an annotated edition of the Principia in Latin, and it was most likely during their conversations that du Châtelet thought of attempting a translation. She was an accomplished translator, fluent in Latin and acquainted with Spanish and Italian. The Principia appealed to her since no version existed in French. The only non-Latin edition had been published in English 15 years earlier. If she could accomplish a French translation, she had a real chance to create something lasting.

The subject matter, too, must have greatly intrigued her. From a young age, du Châtelet was enamored with math and science. Born on December 17, 1706, to a wealthy aristocratic family in Paris, she was the only girl among six children. Her father was a high-ranking baron in the court of Louis XIV. His wealth and status afforded him some of the best tutors for his children. Emilie’s mother also encouraged her intellectual curiosity. In Robyn Arianrhod’s book Seduced by Logic, Emilie’s cousin is cited as remembering how the young Emilie was allowed to argue with her parents and express her own opinions. This was virtually unheard of at a time in which children, especially girls, were expected to be docile and obedient. From the age of 10, Emilie had the freedom to freely explore the family library, which “usurped” three rooms.

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Emilie took full advantage of all her education afforded her. According to a later recollection by Voltaire, as a young woman, Emilie could recite entire passages from Horace, Virgil, and Lucretius, and was acquainted with the philosophy of Cicero. In addition to her language acumen, she was a skilled musician and sang beautifully. Yet nothing thrilled her quite like math and science. “Her inclinations were more strongly bent towards mathematics and metaphysics than any other studies,” remembered Voltaire.

Of course, because she was a woman, Emilie’s access to these disciplines was stunted. She could not join the French Academy of Sciences and could not even join the male philosophes and géomètres as they sat at the Café Gradot and discussed Newton and Galileo. Women were meant to pursue domesticity and society, not math and science. Those were the domain of men.

These barriers frustrated her to no end. “I feel the full weight of prejudice that excludes [women] so universally from the sciences,” she wrote in the preface to her first full translated work, The Fable of the Bees, around 1735. “This being one of the contradictions of this world, which has always astonished me, as there are great countries whose laws allow us to decide their destiny, but none where we are brought up to think…Why do these creatures whose understanding appears in all things equal to that of men, seem, for all that, to be stopped by an invincible force on this side of a barrier; let someone give me some explanation, if there is one.”

For a time, Emilie even tried to do what was expected of her. At 19, she married Florent-Claude, the Marquis du Châtelet-Lomont. Eleven years her senior, Florent-Claude was a colonel in the king’s army and a member of a very old, powerful noble family. Neither had any illusions about the political necessity of their marriage. For several years, Emilie played the dutiful society wife. She bore three children, attended the theater and the opera, gambled at court, and enjoyed all the fine food Paris had to offer.

But by the time she was 26, it was clear du Châtelet was looking for more. The constant entertainment, which she later referred to as “les choses frivoles” (frivolous things), was not enough. “Since I began to live with myself,” she wrote in Fable, “and to pay attention to the price of time, to the brevity of life, to the uselessness of the things one spends one’s time with in the world, I have wondered at my former behavior: at taking extreme care of my teeth, of my hair and at neglecting my mind and my understanding.”

The marquise began to yearn for the intellectual excitement of her childhood studies. In the spring of 1733, she asked Pierre Louis Moreau de Maupertuis, fast becoming the country’s leading scientist, to tutor her in advanced mathematics. Around this time she also met Voltaire. Her choice to take Voltaire as a lover was unusual, since he was of lower rank. But du Châtelet found something in him that she couldn’t find in the “frivolous things” of Paris. Perhaps even more telling, the country’s most famous writer and philosopher found in her a woman who could match him, wit for wit. “There is a lady in Paris, named Emilie, who, in imagination and in reason, surpasses the men who like to think they know a lot about the one and the other,” the poet wrote to a colleague.

Since du Châtelet could not join the scientific community of Paris, she and Voltaire created their own. Both disciples of Newton, they turned their backs on society life and retreated to Cirey to pursue science. They shuttered rooms with curtains to conduct experiments with light beams, and lit massive forges in the forest to study the effects of heat on metal.

As she sharpened her scientific knowledge, du Châtelet proved herself more than capable of the same — and in some cases superior — analysis as her male counterparts. In the summer of 1737, she and Voltaire both entered the Royal Academy’s annual competition. The subject was the nature of fire. Neither won, but du Châtelet became the first woman ever published by the Academy. In passing along du Châtelet’s paper to a colleague, Maupertuis wrote: “Its author is a young woman, of the highest merit, who’s worked on science for several years now, leaving the pleasures of the city and court behind….when you read it, you will find it hard to believe they gave the prize to anyone else.”

* * *

As she sat down to translate the Principia in 1744, du Châtelet had no illusions about how challenging a task she had set for herself. The Principia was notoriously difficult to read, much less translate. In it, Newton had changed the very way the world thought about science.

“Newton set out his approach in the Preface to the Principia: the use of mathematics to develop and explore theories, plus the essential interplay between theory and experiment,” writes Colin Pask in Magnificent Principia. Simply put, it was the first time anyone had tried to apply mathematical theory to all of nature, backed by experimentation and observation.

The Principia contained revolutionary ideas about the nature of gravity, centripetal force and planetary movement. As Arianrhod points out in Seduced by Logic, Newton also stretched the limits of known mathematics, using geometric constructions in place of algebraic equations when discussing geometric shapes. The proofs for such formulas were idiosyncratic and often required the proof of several more propositions, each nested within one another. There were very few mathematicians in the world that could follow it. Du Châtelet struggled through it, but she completed her translation in a year without sacrificing any of her duties as a courtier at Versailles.

Yet, according to Zinsser, something bothered du Châtelet as she worked through the Principia. In several sections, the data wasn’t as clearly corroborated as she would have liked. What’s more, much had been written and published about Newton’s theories in the 62 years since the Principia first appeared, challenging some of its conclusions. Du Châtelet realized that in order to have a proper translation, she had to at least acknowledge the recent advances in the field. In November 1745, she wrote to Jacquier that she had decided to expand the scope of her project. She would now add a commentary, pulling together the last six decades of scientific memoir, as well as many of her own conclusions and observations from her experiments with Voltaire.

Less than a month later, however, the marquise’s project stalled. She discovered that Voltaire had been carrying on a sexual relationship with his niece. Even more painful than the betrayal was the fact that he had hidden it from her for so long. The revelation made du Châtelet sick enough that she put her commentary aside for nearly a year. She later wrote that she had suffered “terrible shocks” which cost her “many tears.”

Eventually, there was nowhere to turn but back to “her Newton,” as she affectionately started calling it. She found the proofs “very boring” and the commentary “very difficult,” as she told Jacquier. But by 1748, the project was taking on a clear shape. By the end of that year, du Châtelet had created a unique, three-part commentary.

The first section was an “abridged Exposition” on Newton’s work, in which she summarized the history of astronomy from the Babylonians to the modern period, and laid out many of the key terms and principles in the Principia. From there, across seven chapters, du Châtelet expanded the scope of Newton’s three proofs of attraction. Among many other propositions, this included her commentary on the “three-body problem,” or the irregularities in the orbits of the sun, moon, and the Earth, as well as the phenomenon of comets returning to Earth’s orbit.

The latter especially excited her as verifiable proof of Newton’s laws of attraction. “The comet of 1680 having so considerable a time of duration, its return that is to take place toward the year 2255, is of little interest,” she wrote. “But there is another comet whose return is so near that it promises a very agreeable spectacle for the astronomers of our time. It is the comet that appeared in 1682, in circumstances so similar to those of the comet that appeared in 1607 that it is difficult not to believe it is not one and the same planet, making its revolution in seventy-five years around the Sun. If this conjecture is found verified, the same comet will reappear in 1758, and this will be a very pleasing moment for the partisans of M. Newton.”

The third and final section of her commentary was the hardest. du Châtelet took the idiosyncratic mathematical proofs relating to the laws of attraction that had been most scrutinized by Newton’s critics and recast his geometrical equations into integral calculus. “This became for her, as it would have been for most géomètres of the day, the most difficult aspect of her project,” writes Zinsser. “When complete, her Commentaire would present Newton’s great work on a number of levels, in addition to the translation itself.”

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Very little stood in the way of her completing it. That is, until 1748, when she met Saint-Lambert at a dinner party. The next year, she discovered she was pregnant. Aside from the social scandal, du Châtelet recognized the pregnancy for what it was: a death sentence. As word spread around Versailles, du Châtelet put all of her energies toward finishing her commentary. But it started to exact a toll. “I do not love Newton,” she wrote Saint-Lambert. “At the least I finish it out of a sense of duty and of honor, but I only love you and what relates to you.” Still, it had taken her five years, and she was determined to see it done. She sequestered herself from everyone and everything, except Clairut, who checked her math, and occasionally Voltaire, with whom she still shared a home.

Before giving birth, the marquise was transferred to the palace at Lunéville, in northeastern France, where she and Voltaire regularly stayed with Stanislas Leszczyński, the deposed king of Poland, and his court. Voltaire, her husband and Saint-Lambert all attended her there. At four in the morning on September 4, after a relatively easy labor, du Châtelet gave birth to a daughter, christened Stanislas-Adélaïde. For a few days afterward, du Châtelet seemed to be fine. But unbeknownst to anyone, a pulmonary embolism had formed in her lung. The marquise was slowly suffocating.

On September 10, du Châtelet took an unexpected turn for the worse. A violent headache gave way to difficulty breathing. The king’s doctor was concerned enough that he sent for two more physicians. After some opiates, she calmed down, and everyone except Saint-Lambert and two servants went to dinner across the courtyard. Saint-Lambert had just stepped outside her room when she started gasping for breath. By the time he burst back in, she was already gone.

“When the others arrived, in tears, they found a ghostly Saint-Lambert paralyzed with shock,” writes Arianrhod. “The marquis du Châtelet was so upset he could not stand up, while Voltaire sobbed uncontrollably. A little later, he raged at Saint-Lambert like a madman, accusing him of killing his beloved Emilie.”

Eighteen months later, Stanislas-Adélaïde also died. With the king’s permission, both mother and daughter were buried together at Lunéville, in a grave marked by a blank marble slab at the entrance to the king’s new church of Saint-Jacques.

* * *

Had things gone differently, du Châtelet would have lived to see her Principia commentary published, as well as witness the return of Halley’s Comet to Earth’s atmosphere herself. In 1759, Clairut calculated the comet’s arrival within a month of its actual appearance in March. It was he who arranged the marquise’s commentary for publication and dissemination. When he did, as Zinsser notes, “du Châtelet’s ‘Newton,’ with its unique three-tiered commentary, became for a whole generation of French physiciens and géomètres their principal means of access to the Principia.”

Emilie du Châtelet defied the conventions of her time. She recast what it meant to be both a woman and a mathematician in an era that strictly defined each. While her Principia remains her greatest and most lasting work, she left behind an entire body of writing filled with wit, wisdom and a desire to see women rise to a status that she herself could only dream of.

One of her final essays, Discourse on Happiness, was written during her messy break with Voltaire and finished sometime around 1748 as a gift to Saint-Lambert. In it, she extols the value of study for women, especially those who wish to be independent: “Women are excluded, by definition, from every kind of glory, and when, by chance, one is born with a rather superior soul, only study remains to console her for all the exclusions and all the dependencies to which she finds herself condemned by her place in society.”

The same essay concludes: “Above all, let us be certain of what we want to be; let us choose for ourselves our path in life, and let us try to strew that path with flowers.”

Matt Grant is a staff writer for LitHub, and his work has appeared in Longreads, Tor.com, and The Brooklyn Rail, among others. He lives in Brooklyn with his wife and every other writer in the world.