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Illuminator of the Enlightenment

Name: Émilie du Châtelet
Nationality: French
Lived: 1706-1749
Fields: Mathematics and physics
Claim to fame: A major figure of the Enlightenment

Through their intellectual salons, women played a pivotal role in spreading the ideas of the European Enlightenment. However, one woman not only illuminated the Enlightenment

through her writings, but also made her own lasting contributions to the quest for reason and science. She was the French mathematician, physicist and author Émilie du Châtelet (1706-1749).

Between reason and romance

Gabrielle Émilie le Tonnelier de Breteuil, Marquise du Châtelet, was born in 1706. Later known simply as Émilie du Châtelet, she was the daughter of Louis Nicolas le Tonnelier de Breteuil, King Louis XIV’s principal secretary. Her father’s position gave the family some standing and provided Émilie with access to France’s aristocratic and intellectual elites early in life.
Recognising Émilie’s brilliance from a young age, her father – unusually for the times – arranged training for her from early childhood in physical activities, such as fencing and riding. As she grew older, he brought tutors to the house who educated her in mathematics, literature and science. In addition, Bernard le Bovier de Fontenelle, who wrote popular text books on astronomy which took the form of a conversation between a teacher and a (female) student, schooled her in astronomy when she was ten.
Émilie’s mother, Gabrielle-Anne de Froulay, who was brought up and educated in a convent, did not approve of her daughter’s intellectual pursuits, but the investment paid off. By the time she was 12, Émilie was fluent in Greek, Latin, Italian and German. She was not just an intellectual but also a ‘party animal’. She liked to dance, could play the harpsichord, sang opera, was an amateur actress and a ‘calculated gambler’.

Traditional husbands, enlightened lovers

Despite her unconventional mind and lifestyle, Émilie settled for a conventional aristocratic marriage. In 1725, she married the Marquis Florent-Claude du Chastellet (or Châtelet). After the birth of their two sons and daughter, Émilie and her husband made an agreement – common among the French aristocracy at the time – to live separate lives, including taking lovers, while still maintaining one household.
At the age of 25, in 1730, Émilie kicked off her affairs with the Duc de Richelieu (grand-nephew of the famous cardinal of the same name) who was drawn by Du Châtelet’s passion for literature and philosophy. But her most well-known lover was the fourth, in an affair which began in 1733. It was with Voltaire, the famous Enlightenment writer, who used to frequent her father’s salons when she was younger. Émilie sheltered Voltaire, who was being pursued by the authorities for his controversial political views, in her country estate.
For 15 years, the couple lived together in a passionate meeting of minds and hearts. In addition to publishing works on physics and mathematics, they built up a collection of 21 000 books which was larger than the libraries of most European universities. Voltaire’s admiration for Émilie was boundless. He declared in a letter that she was “a great man whose only fault was being a woman”.
During Émilie’s last love affair she fell pregnant and puerpural fevers led to the death of her and her newborn days after the birth, in 1749. She was just 42.

The nature of intellectual light

Due to the constraints imposed on women by French society at the time, Émilie du Châtelet was unable to follow a similar education to her male counterparts. However, her genius, resourcefulness, voracious appetite for knowledge acquisition, and her father’s early enlightened assistance helped her to overcome these challenges.
Émilie considered her marital responsibilities fulfilled once her third child was born. Thereafter, she dedicated herself to the pursuit of knowledge and romance. In 1737, she published a paper on the nature of fi re in which she described what we call today infrared radiation, as well as refl ecting on the nature of light.
In 1738, she and Voltaire published their successful joint work, Elements of Newton‘s philosophy. Their co-operation led Voltaire to recognise Émilie’s superior intellect, especially when it came to physics. A decade after the book was published, he confided: “I used to teach myself with you, but now you have flown up where I can no longer follow.”

Energetic works

Two years later, in 1740, she published Institutions de physique (Lessons in physics). The book sought to reconcile complex ideas from the leading thinkers of the time, including the German, Dutch and English philosophers and mathematicians Gottfried Leibniz, Willem ‘s Gravesande and Isaac Newton. She showed that the energy of a moving object is proportional not to its velocity, as had previously been believed, but to the square of its velocity.
The final year of her life coincided with the completion of what is widely regarded as her opus magnum: her translation into French and commentary on Newton’s Principia Mathematica. She even managed to extrapolate from Newton’s principles of mechanics the notion of the conservation of energy.

Scientific achievements

Émilie du Châtelet can rightly be regarded as one of the principal illuminators of the Enlightenment. Her works helped disseminate the new physics, mathematics and general philosophy of the age. In addition, she made some significant discoveries and developed a number of important concepts in her own right, such as infrared radiation and energy conservation.
Despite the admiration and esteem she was held in by major intellectual figures of the time, her gender elicited ridicule among otherwise enlightened men.