**Lived 1700 – 1782.**

Daniel Bernoulli published his masterpiece *Hydrodynamica* in 1738 only to see it plagiarized by his own jealous father. Bernoulli explained how the speed of a fluid affects its pressure – the Bernoulli Effect explains how an airplane’s wings generate lift. Bernoulli’s kinetic theoryanticipated James Clerk Maxwell’s by more than a century, and Bernoulli carried out ground-breaking work on the theory of risk, utilized in areas as diverse as economics and evolution.

### Beginnings

Daniel Bernoulli was born in the city of Groningen in the Netherlands on February 8, 1700.

His parents were Johann Bernoulli and Dorothea Falkner.

**Mathematics was in their Blood**

Daniel’s mother Dorothea Falkner came from a well-known and wealthy family in Basel, Switzerland.

Daniel’s father Johann Bernoulli also came from Basel, and was a qualified medical doctor and brilliant mathematician, one of the first to master and expand the new mathematics of calculus. Johann’s reputation was so high that he was called the “Archimedes of his age.”

Not surprisingly, with a father like Johann, Daniel made rapid progress in mathematics. Daniel’s two brothers became first-rate mathematicians too. Daniel was probably taught more by his older brother Nicolaus than his father, who, although brilliant, could be unsympathetic and hard on Daniel.

Mathematics seems to have run in the Bernoulli family, because Johann’s older brother Jacob was also a brilliant mathematician.

**Whatever You Do, Don’t Become a Mathematician!**

Daniel’s father held the chair of mathematics at the University of Groningen.

In 1705, when Daniel was aged 5, his family relocated to Basel in Switzerland, his parents’ hometown, where his father would became chair of mathematics at Basel University.

Despite the high reputation he enjoyed as a mathematician, Daniel’s father resented the low pay he felt mathematicians received. The Bernoulli family had once been wealthy merchants and Daniel’s father believed Daniel had the personal qualities needed to return the family to its gloriously wealthy past.

He pushed a reluctant Daniel to study business. Daniel, however, had a burning passion for mathematics. After some toing and froing – they were both rather obstinate – father and son reached a compromise: Daniel would study medicine.

**Bernoulli’s European Tour**

Daniel was as good as his word. Beginning at the age of 15 he studied medicine in Heidelberg in Germany; Strasbourg in France; and Basel in Switzerland. His father, happy that Daniel was fulfilling his part of the bargain, agreed to teach him advanced mathematics and physics – particularly his ideas about the conservation of energy.

**Bizarre Selection Process **

Daniel Bernoulli graduated as a doctor of medicine in 1721, aged 21, with a thesis on respiration.

He hoped to get a job teaching at the University of Basel, but lost out in a bizarre selection procedure where candidates drew lots to see who would get the teaching jobs.

While trying and failing to find work in Basel, Bernoulli continued studying mathematics.

**Bernoulli’s Tour and Mathematics Infatuation Continue**

In 1723 Bernoulli moved to Venice in Italy to learn practical medicine. He visited patients and worked in hospitals alongside doctors. He also spent time going to the opera, theater and fancy-dress parties.

However, he could not abandon his love of mathematics – particularly applied mathematics – in which, following in the footsteps of Galileo and Newton, he was eager to engage the power of mathematics in unraveling the secrets of the universe.

Bernoulli carried out fluid mechanics experiments in which he measured water flowing out of a vessel. He noticed that the water flowed out faster as the height of the liquid in the vessel was increased. Potential energy is converted to kinetic energy. He established a mathematical relationship between the height of the water in the vessel and its pressure and its velocity flowing from the vessel.

In 1724 he published his first work, *Mathematical Exercises* in which he made useful contributions to the sciences of fluid mechanics, probability theory, differential equations, and geometry.

**A Prize and a Professorship**

While in the famous seafaring city of Venice, Bernoulli learned that the Paris Academy was offering a generous prize for the best design of a sand-clock to be used for timekeeping at sea. His response was to cleverly design an hour glass whose trickle of sand was unaffected by rough seas. For this work he was awarded the Grand Prize. This, combined with his *Mathematical Exercises*, which had been well received, won him the offer of a professorship at the Academy of Sciences in Saint Petersburg, Russia.

Given his medical background, he was appointed as a professor of physiology, not mathematics.

He and his older brother Nicolaus, who *had* been offered a mathematics professorship at St Petersburg, traveled there together in 1725.

**Saint Petersburg**

Bernoulli’s first works in St Petersburg reflected his position – he wrote papers on topics such as the optic nerve, muscles, and medical mathematics.

Although in his later years Bernoulli was reported to be easy going, this was not the case at first at the Academy, where he got into some fierce academic disagreements with other professors.

Unfortunately, less than a year after arriving in Russia, Nicolaus died of fever. Daniel was miserable and the bitter weather in Russia did not improve his spirits.

His father tried to help, sending his best mathematics student, Leonard Euler, to St Petersburg to work with his lonely son.

Euler, whose name would soon be revered as one of the greatest mathematicians in history, reached St Petersburg in 1727. Not only did he bring the tea, coffee and brandy that Bernoulli longed for, the pair of them were soon happily exchanging ideas, inspiring Bernoulli to do the best work of his career.

It should be remembered that Daniel Bernoulli was brilliant in his own right, independent of Euler. He showed particular genius in his ability to perform meaningful experiments and to translate his observations into physical laws and mathematics. Euler, a more powerful mathematician, could refine Bernoulli’s mathematics.

In 1730 Bernoulli was appointed professor of mathematics at the Academy, but by then he was already planning to leave.

## Daniel Bernoulli’s Contributions to Science

Many of Bernoulli’s greatest discoveries were contained in his masterpiece on fluid mechanics – *Hydrodynamica*, completed in St Petersburg in 1733 and tidied up for publication in Strasbourg in 1738.

### The Kinetic Theory of Gases

Early in the 1700s some scientists, led by James Hermann, had begun to believe that matter is made up of small moving particles. The more rapid the movement, the greater the temperature.This type of kinetic theory remained controversial until it was universally accepted in the 1800s.

In 1729 Euler made an attempt to explain the behavior of gases mathematically with a kinetic theory based on Robert Boyle’s gas data from 1662. He assumed, incorrectly, the gas particles would all travel at the same speed.

Bernoulli’s stroke of genius was to see that the particles would have a distribution of different speeds.

His skill in interpreting the way the physical world works allowed him to introduce a mathematical statistical factor into kinetic theory, anticipating the work of James Clerk Maxwell over a century later.

### The Bernoulli Effect

Bernoulli returned to the ideas he had first learned from his father and developed them. He applied the idea of energy conservation to fluids in motion.

In doing so he discovered The Bernoulli Effect – the discovery he is most famous for – that when a fluid flows through a region in which its speed increases, its pressure will fall. He correctly described the effect mathematically.

The Bernoulli Effect has many real-life applications and is often cited as the reason aircraft wings provide lift.

### Measurement of Risk

In the early 1730s Bernoulli wrote a paper in a totally different field from his usual mechanics. Again it took him until 1738 to publish it – *Exposition of a New Theory on the Measurement of Risk*. Bernoulli used the geometric mean of data to assess risk; how to minimize risk; and situations in which risk is best avoided altogether.

The paper looked at the difference between wealth and utility and influenced economic and portfolio theory, evolutionary biology and behavioral ecology.

### Some Personal Details and the End

Bernoulli could never settle in St Petersburg and his health was never good there.

He arrived back in Basel in 1733 to begin a new role as chair of anatomy and botany. In the same year his entry for the Grand Prize of the Paris Academy – a work on the inclinations of the planets’ orbits – finished joint-first.

This turned out to be not entirely good news. The trouble was that he shared the prize with his father, who was outraged that anyone could judge his son to be his equal. From that time on, father refused to speak to son.

Daniel’s masterpiece *Hydrodynamica* was finally published in 1738, although it had been completed and submitted to the Academy in St Petersburg in 1733. In a despicable act of vengeance, his father plagiarized *Hydrodynamica* and released a book called *Hydraulica*, which he dated as completed in 1732.

Daniel was shocked by his father’s behavior, writing:

*Hydrodynamica*, not one part of which I owe to my father and I have been deprived of the fruits of 10 years of work.”

Thankfully for Daniel, he was judged to be the true originator of the ideas in the book.

Daniel won the Paris Academy’s Grand Prize a total of 10 times, often for nautically themed work, including: the best shape for a ship’s anchor; theory of the tides; magnetism; ocean currents; and improving the stability of ships in high seas.

In 1750, aged 50, Daniel Bernoulli was appointed to the chair of physics at the University of Basel. His lectures and demonstrations were enormously popular, and he continued in this position until he retired at the age of 76.

He received offers of chairs in other cities, but never left Basel again. He corresponded extensively with other scientists, of whom his favorites were Pierre Bouguer, Alexis Clairaut, Pierre Louis Maupertuis, his old friend Leonhard Euler, and Euler’s son Johann Euler.

He lived for his work; he never married and had no children. He had considered marriage when he was younger, but the woman in question turned out to be very mean with money, which he found off-putting. Bernoulli respected simplicity of lifestyle and frugality, but not meanness.

In the end, he valued his freedom and a quiet, peaceful, academic way of life too much to marry.

Daniel Bernoulli died in his sleep aged 82 on March 17, 1782 in Basel, Switzerland.

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**Further Reading**

Danielis Bernoulli

Hydrodynamica, sive De viribus et motibus fluidorum commentarii. Opus academicum ab auctore, dum Petropoli ageret, congestum

Johannis Reinholdi Dulseckeri, 1738

Daniel Bernoulli, translated by Louise Sommer

Exposition of a New Theory on the Measurement of Risk

Econometrica, Vol. 22, No. 1. pp. 23-36, January 1954

Volker Zimmermann, David Speiser, Fritz Verzar, Gleb K. Mikhailov, Otto Spiess-Stiftung, Mario Howard-Haller

Die Werke von Daniel Bernoulli: Band 1: Medizin und Physiologie, Mathematische Jugendschriften, Postitionsastronomie

Springer Science & Business Media, 1996

Stephen C Stearns

Daniel Bernoulli (1738): evolution and economics under risk

J. Bioscience Vol. 25, No. 3. pp. 221 – 228, September 2009

C. Truesdell

Essays in the History of Mechanics

Springer Science & Business Media, 2012