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1. Émilie du Châtelet
Émilie du Châtelet, famous for being Voltaire’s mistress, was actually a talented scientist
and intellectual in her own right. Overcoming challenges that kept women from becoming
scientists at the time, she educated herself and carried out experiments in physics, and
completed a translation and commentary on Newton’s Principia.
Gabrielle Émilie le Tonnelier de Breteuil (later Émilie du Châtelet), was born December 17,
1706 in Paris. Her father, Louis Nicolas le Tonnelier de Breteuil, was a high ranking official of
the court of Louis XIV. The de Breteuil family was part of French aristocratic society, and as
such they entertained often. Distinguished scientists and mathematicians were frequent
visitors to the household.
Educated at home, the young Émilie learned to speak six languages by the time she was
twelve, and had lessons in fencing and other sports. Even from a young age she was
fascinated most by science and math, much to her mother’s displeasure. Such interests
were not viewed as proper for young ladies, and her mother even threatened to send her
away to a convent. Fortunately, her father recognized her intelligence and encouraged her
interests, arranging for her to discuss astronomy with prominent scientists he knew.
Émilie also had a flair for gambling, applying her talent at mathematics to give herself an
advantage. She used her winnings to buy books and laboratory equipment for her scientific
investigations.
When she reached age 18, she knew she had to get married, and she accepted the proposal
of Marquis Florent-Claude du Châtelet, a distinguished army officer. This was a convenient
arrangement for Émilie, because Châtelet was often away from home, leaving her free to
indulge her interests in studying math and science on her own.
She was also free to carry on an affair with the writer Voltaire, one of the few men who
appreciated her intelligence and encouraged her scientific pursuits. Émilie du Châtelet and
Voltaire renovated Châtelet’s large estate house in the countryside. The house included
several rooms for scientific equipment and space for experiments, and a large library
holding over 20,000 books, more than many universities at the time.
Although she was frustrated at being excluded from scientific society and education because
she was a woman, she was able to learn mathematics and science from several renowned
scholars, including Pierre-Louis Maupertuis and Samuel Konig, by inviting them to her
house.
In 1737, after several months of conducting research in secret, she entered a contest
sponsored by the French Academy of Sciences on the nature of light, heat and fire,
submitting her paper Dissertation sur la nature et la propagation du feu. In it she suggested
that different colours of light carried different heating power and anticipated the existence

2. of what is now known as infrared radiation. She did not win the contest, but her paper was
published and was positively received by the scientific community.
She also developed a strong interest in the work of Isaac Newton, which was somewhat
controversial at the time in France, where Cartesian philosophy was favoured over
Newton’s ideas. Émilie and Voltaire jointly wrote a book, Elements of Newton’s Philosophy,
which explained Newton’s astronomy and optics in a clear manner for a wide French
readership. Only Voltaire’s name appeared on the book, but he acknowledged her
important role.
Émilie also worked on another manuscript, Foundations of Physics, in which she considered
the philosophical basis of science and tried to integrate the conflicting Newtonian,
Cartesian, and Leibnizian views.
One of her most important contributions to science was her elucidation of the concepts of
energy and energy conservation. Following experiments done earlier by Willem Gravesande,
she dropped heavy lead balls into a bed of clay. She showed that the balls that hit the clay
with twice the velocity penetrated four times as deep into the clay; those with three times
the velocity reached a depth nine times greater. This suggested that energy is proportional
to mv2
, not mv, as Newton had suggested.
While conducting her scientific work, Émilie du Châtelet still carried out her duties as a
mother to her three children and as a hostess for her many visitors so she was always busy,
and had little time for sleep.
At age 42, Émilie du Châtelet discovered she was pregnant. At that time, a pregnancy at
such an old age was extremely dangerous. Knowing she would likely die, she began working
18 hours a day to complete her biggest project, a French translation of Newton’s Principia,
before she died.
More than simply a translation, Émilie du Châtelet’s Principia included her own notes,
examples, derivations, and clarifications of Newton’s often obscure writing, as well as
examples of experiments that confirmed Newton’s theories. Her modern notation and clear
style soon helped French scientists understand and build upon Newton’s ideas.
With determined effort, she achieved her goal of finishing the manuscript just before she
died in September 1749. The complete work was published ten years later, when the return
of Halley’s Comet brought about a renewed interest in Newtonian mechanics.
Émilie du Châtelet’s book was for many years the only available translation of Newton’s
Principia into French, and the translation and insightful commentary probably helped
advance science in France. Nonetheless, Émilie du Châtelet herself was largely forgotten by
history (or remembered mainly as Voltaire’s mistress) and only recently have her scientific
achievements been brought to light.

3. ***
Agnes Pockels
With no formal training in chemistry, Agnes Pockels initially carried out experiments in her
kitchen, later being recognised as a pioneer of surface science.
Agnes was born in 1862 in Venice, which at that time, was under Austrian rule. Her father
served in the Austrian army, but when he fell ill with malaria, the family moved to Brunswick
in the newly-formed German Empire. Agnes was interested in science as a child but her local
girls’ school, which she attended, did not have much science on the curriculum.
“I had a passionate interest in natural science, especially physics, and would have liked to
study,” Agnes Pockels is reported to have said.
Despite Agnes's desire to study physics after leaving school, women were not allowed to
enter the universities. Her younger brother Friedrich, however, also wanted to study physics
and took a degree at the University of Göttingen. By sending letters to his sister and giving
her access to his textbooks, Friedrich helped Agnes learn advanced physics from her home
in Brunswick. Friedrich became a physicist and throughout his life he sent Agnes letters
detailing the latest developments in physics.
Despite her studies at home, Agnes was not able to perform the experiments that her
brother could due to a lack of equipment. Nonetheless, her day-to-day activities running her
family home provided occasional chances to put her education to good use; legend has it
that she became interested in the effect of impurities on the surface tension of liquids while
doing the washing up in her kitchen. As she looked after the house of her ageing parents,
she had lots of opportunities to use soaps, oils and other products, and to see the effect
they had on water.
Not long after, she developed a piece of apparatus called the Pockels trough; although
simple, this trough was able to measure the surface tension of water under the influence of
different surface concentrations of the oils and soaps she worked with.
After a couple of years of experimentation with the Pockels trough, Agnes received a letter
from her brother telling her about a publication by Lord Rayleigh. In this paper, Rayleigh had
investigated the properties of a thin layer of oil on the surface of water. Seeing that Rayleigh
was conducting similar research to her own, Agnes sent him a letter, in German, with the
results of her experiments. She told Rayleigh he could keep her results for himself, but he
was so impressed, he had the letter translated and submitted it to the journal Nature under
her name, together with an article of his own. He wrote to them saying, “I shall be obliged if
you can find space for the accompanying translation of an interesting letter which I have
received from a German lady, who with very homely appliances has arrived at valuable

4. results respecting the behaviour of contaminated water surfaces.” Nature published the
letter, and Pockels’s work became renowned.
She continued to perform experiments in her kitchen, and with Rayleigh’s encouragement,
went on to publish several more papers on surface science. Unfortunately the health of her
parents worsened shortly after the turn of the century, leaving less time for her to study,
and the First World War hit her social and scientific circles hard. She stopped performing
experiments after the war, and maintained only intermittent contact with scientists in her
field.
The Pockels trough was adapted and developed by Irving Langmuir, who then used it to
make several more important discoveries in surface science. He received the Noble Prize for
these discoveries in 1932, and in an article he paid tribute to Agnes’s work. Two
commentators, Charles Giles and Stanley Forrester, later wrote: “When Langmuir received
the Nobel Prize for Chemistry in 1932, for his work in investigating monolayers on solids and
on liquids, part of his achievement was thus founded on original experiments first made
with a button and a thin tray, by a young lady of 18 who had had no formal scientific
training.”
However, Agnes's work did not go unrecognised during her lifetime. In 1931, she was
awarded the Laura R. Leonard Prize of the German Colloid Society, the first woman to win
the award. The following year, she received an honorary doctorate from the Technical
University of Braunschweig, in honour of her 70th birthday.
Agnes died shortly after these awards, in 1935. Just before her death, the eminent biologist
Sir William Bate Hardy FRS, wrote: “I think I may say without exaggeration that the immense
advances in the knowledge of the structure and properties of this fourth state of matter,
which have been made during this century, are based upon the simple experimental
principles introduced by Miss Pockels.”
***
Henrietta Swan Leavitt
Henrietta Swan Leavitt was a Harvard "computer" — one of several women in the early
1900s who studied photographic plates for fundamental properties of stars. Leavitt is best
known for discovering about 2,400 variable stars between 1907 and 1921 (when she died).
She discovered that some of these stars have a consistent brightness no matter where they
are located, making these so-called Cepheid variables a good measuring stick for
astronomical distances. Her work helped American astronomer Edwin Hubble measure
galaxy distances in the 1920s, which led to his realization that the universe is expanding.
Leavitt was born on July 4, 1868, and was educated at both Oberlin College and the Harvard-
affiliated Radcliffe College (then known as the Society for the Collegiate Instruction of

5. Women). She became a volunteer assistant at the Harvard College Observatory and was
subsequently employed in 1907 (according to Harvard) under director Edward Charles
Pickering, who hired dozens of females during his decades-long tenure at the observatory.
While Pickering's effort was noteworthy for an era where few women worked outside the
house, the work he hired them for – analyzing photographic plates – was long and tedious,
and the pay was cheaper than what a man would have been offered. Leavitt was put to
work analyzing the brightness of stars using the plates; to do comparisons, she would often
overlay one plate on top of another to see how the star had changed its brightness between
exposures.
It was while Leavitt did this work that she discovered that some stars have a consistent
brightness no matter where they are located – making it easy to figure out their distance
from Earth. Instead of offering wild estimates for how far objects were from us, it was now
possible to more precisely measure their distances. Leavitt had become, in the words of
George Johnson, author of the book "Miss Leavitt's Stars" (Norton, 2006), "the woman who
discovered how to measure the Universe," according to a biography of her by the American
Association of Variable Star Observers (AAVSO).
Leavitt, however, reportedly received little credit for her work at the time. Pickering
published what she had found, but used his own name for the work, AAVSO said; Leavitt
was mentioned only as the person who had prepared the information. A few years later, the
new director Harlow Shapley used Leavitt's work to figure out distances around the Milky
Way, and didn't give Leavitt a lot of credit, AAVSO added.
"Little is known of Henrietta Leavitt's personal feelings about the way she had been
overstepped," AAVSO wrote. "Hers was a shy and somewhat unassuming personality, and
women at that time, even highly educated and brilliantly talented women who in a fairer
world would have been respected as equals by their male peers, were all too often resigned
to taking a lesser role, and were often just quietly grateful to be given any sort of role at all."
Leavitt's legacy
Leavitt died in 1921 as a mostly unknown astronomer, something that several biographies
are working to correct today. After her death, her findings soon sparked a new
understanding of the universe. Besides the work performed by Shapley, another American
astronomer, Edwin Hubble, used Leavitt's information to help him understand the distance
to the nearest large galaxy to Earth, known as the Andromeda Galaxy (more officially known
as M31).
Andromeda's distance of 2.5 million light-years was established in the 1920s using Cepheid
variables, making it clear the galaxy was far outside the boundaries of the Milky Way. In
other words, Hubble determined that there were other galaxies like our own in the
universe. Subsequently, Hubble figured out that the universe was expanding by measuring

6. the "redshift" of receding stars whose light was being pulled to the red side of the light
spectrum.
"Leavitt's discovery was so important that in 1924, Gösta Mittag-Leffler of the Swedish
Academy of Sciences tried to nominate her for the Nobel Prize," an article in Air and Space
Smithsonian stated. "Unfortunately, Henrietta died of cancer three years before this, and
the Nobel Prize is not awarded posthumously."
Cepheid variables are still used today to help us understand the distance to astronomical
objects. As astrophotography techniques continue to improve, these distances are refined.
A famous example took place in 2012, when it was revealed that the North Star Polaris – a
nearby Cepheid variable — is about 100 light-years to Earth closer than thought.
After Leavitt’s death in 1921, Edwin Hubble used the relationship between the period and
luminosity of the Cepheid variables to determine that the universe was expanding. Decades
later in the 1990s, astronomers built on this work by discovering that the expansion is, in
fact, accelerating. In 2011, the Nobel Prize in Physics was awarded for this discovery.
One of those Laureates, Adam Riess, had used and extended Leavitt’s tool as a graduate
student doing cosmology research at CfA. Only two years after graduating he led a paper
reporting the discovery of the universe’s accelerating expansion. “By discovering a
relationship for some stars between how bright they appear and how fast they blink,
Henrietta Leavitt gave us a tool to gauge the size and expansion rate of the universe,” Reiss
said. “That tool remains to this day one of our very best for studying the universe.”
Leavitt discovered how to determine the size of the universe and distance between the stars
by stacking glass plate photos of the night sky taken at different times and comparing
brightness.
Leavitt’s legacy continues to this day. For example, a Hubble Space Telescope result
announced in January 2018 highlights the use of her relationship — now generally called
Leavitt’s Law — in on-going attempts to identify whether new physics has been uncovered
in recent cosmology observations.
As with many other female scientists of her time, Leavitt’s contributions to her field went
largely unacknowledged by the scientific peers.
***
Janaki Ammal
One of the first women scientists to receive the Padma Shri way back in 1977, Edavaleth
Kakkat Janaki Ammal lived a life only a handful of other women of her time lived. In an age
when most Indian women didn’t make it past high school, Janaki Ammal didn’t just obtain a
PhD at one of America’s finest public universities, she went on to make seminal

7. contributions to her field. She also remains one of the few Asian women to be conferred an
honorary doctorate (DSc. honoris causa) by her alma mater, the University of Michigan. And
that was in 1931!
A pioneering botanist and cytogeneticist, Janaki Ammal is credited with putting sweetness in
India’s sugarcane varieties, speaking against the hydro-electric project in Kerala’s Silent
Valley and the phenomenal study of chromosomes of thousands of species of flowering
plants. There is even a flower named after her, a delicate bloom in pure white called
Magnolia Kobus Janaki Ammal.
EK Janaki Ammal was born in Tellichery (now Thallassery) in Kerala on November 4, 1897.
Her father, Dewan Bahadur EK Krishnan, was a sub-judge in what was then the Madras
Presidency. A man with a keen interest in the natural sciences, Janaki’s father would
correspond regularly with scholars of the time and maintain descriptive notes about his
developing garden. This love for learning and curiosity about the natural world was
something he would pass on to his 19 children — six from his first wife, Sharada, and
thirteen from the second, Deviammal, the tenth of whom was Janaki Ammal.
After completing her schooling in Tellichery, Janaki moved to Madras where she obtained
her Bachelor’s degree from Queen Mary’s College and her Honours degree in Botany from
the Presidency College in 1921. She was teaching at Women’s Christian College when she
got the prestigious Barbour scholarship from the University of Michigan in the US.
Choosing a life of scholarship over marriage (which was being planned to a first cousin),
Janaki left for the University of Michigan, where she obtained her Master’s degree in 1925.
Returning to India, she continued to teach at the Women’s Christian College, but went to
Michigan again to pursue her doctoral thesis. On her return, she became Professor of
Botany at the Maharaja’s College of Science in Trivandrum, and she taught there for two
years between 1932 and 1934.
An expert in cytogenetics (the study of chromosomes and inheritance), Janaki next joined
the Sugarcane Breeding Station at Coimbatore to work on sugarcane biology. At that time,
the sweetest sugarcane in the world was the Saccharum officianarum variety from Papua
New Guinea and India imported it from Southeast Asia. In a bid to improve India’s
indigenous sugarcane varieties, the Sugarcane Breeding Station had been set up at
Coimbatore in the early 1920s.
By manipulating polyploid cells through cross-breeding of hybrids in the laboratory, Janaki
was able to create a high yielding strain of the sugarcane that would thrive in Indian
conditions. Her research also helped analyse the geographical distribution of sugarcane
across India, and to establish that the S. Spontaneum variety of sugarcane had originated in
India.

8. In 1935, C V Raman founded the Indian Academy of Sciences and selected Janaki as a
research fellow in its very first year. However, her status as a single woman from a caste
considered backward created irreconcilable problems for Janaki among her male peers at
Coimbatore. Facing caste and gender based discrimination, Janaki left for London where she
joined the John Innes Horticultural Institute as an assistant cytologist, where she stayed
from 1940 to 1945.
Impressed by her work, the Royal Horticulture Society invited Janaki to work as a cytologist
at their campus at Wisley, near Kew Gardens, famous for its collection of plants from around
the world. It was during her years at Wisley that Janaki met some of the most talented
cytologists, geneticists and botanists in the world. In 1945, she co-authored The
Chromosome Atlas of Cultivated Plants with biologist CD Darlington, a close friend and
mentor for the greater part of her life.
At the Society, one of the plants she worked on was the magnolia. To this day, in the
Society’s campus at Wisley there are magnolia shrubs she planted and among them is a
variety with small white flowers named after her: Magnolia Kobus Janaki Ammal. A flower
celebrated in Japanese and Chinese legends, the blooms of this variety are made up of fused
sepals and petals called ‘tepals’. Today, only a few nurseries in Europe cultivate the variety.
In 1951, the then prime minister Jawaharlal Nehru personally invited her to return to India
and restructure the Botanical Survey of India (BSI). She acquiesced and was appointed as the
Officer on Special Duty to the BSI, in which capacity she reorganised the Calcutta office in
1954. Her colleagues still remember how Janaki would take a long broom and clean the
streets outside the BSI office on the famous Chowringhee lane.
Janaki also travelled to some of the most remote areas of the country in search of the plant
lore of the indigenous peoples of the subcontinent. She would spend time searching for
medicinal plants in Wayanad before visiting Ladakh to explore methods of sustainable
agriculture at high altitudes. As a scientist who studied about ecology and biodiversity,
Janaki had always been an ardent environment activist too.
Worried about the environmental damage that would be caused, she played an important
role in the protests that were held against the building of a hydro-power dam across the
river Kunthipuzha in Kerala’s Silent Valley. She was also the only woman invitee to the
landmark international symposium on environmental history, “Man’s Role in Changing the
Face of the Earth” organized by the Wenner Gren Foundation for Anthropological Research
at Princeton in 1955 (and one of only two Indians, the other being Radhakamal Mukherjee).
On a personal note, Janaki was a staunch Gandhian who liked her life simple. Geeta Doctor,
Janaki’s niece, once wrote of her: “Janaki was a tall and commanding presence in her
prime…In her later years, she took to wearing brilliant yellow silk sarees with a long loose
blouse or jacket in the same colour. Her statuesque presence reminded people of a

9. Buddhist lady monk. Like certain Buddhist orders, she took a vow of chastity, austerity and
silence for herself, limiting her needs to the barest minimum.”
After retirement, she continued to work in science; she served for a short period at the
Atomic Research Station at Trombay before serving as an Emeritus Scientist at the Centre
for Advanced Study in Botany, University of Madras. Few know that during her last years,
Janaki’s main interest had been the rearing of a large family of cats and kittens – an expert
geneticist, she had even discovered and tracked down the subtle differentiations in the
characteristics of her beloved kittens!
At the age of 87, Janaki Ammal passed away on February 7, 1984 while working in her
research lab at Maduravoyal. Her obituary stated “She was devoted to her studies and
research until the end of her life.”
For her exemplary contribution to science in India, Dr Janaki Ammal awarded the Padma
Shri in 1977. In 2000, the Ministry of Environment and Forestry created the National Award
of Taxonomy in her name. There is also a herbarium with over 25,000 species in Jammu
Tawi that is named after this pioneering botanist.
Recently, the John Innes Centre in England chose to honour Janaki by launching a new
scholarship for post-graduate students from developing countries in her name.
***