**David Enskog** was a Swedish mathematical physicist who helped develop the kinetic theory of gases.

- Enskog was by this time around six years older than those entering secondary school so he thought that he had missed his chance.
- The chemist who owned the shop then made strenuous attempts to make it possible for Enskog to continue his education.
- The chemist also helped provide Enskog with books for his studies and through 1900 Enskog worked on his own to bring himself up to the level of the fifth year of secondary school.
- It was about 45 km south of his home village so there was no possibility that Enskog could live at home.
- At the secondary school in Karlstad, despite entering into the sixth year, Enskog was still older than others in his class.
- The secondary school ran a nine year programme so Enskog still had four years of schooling to complete.
- Most precious of all for Enskog was the fact that he was now free from the severe restraints imposed by his upbringing and he could make his own decisions.
- How did the freedom affect Enskog?
- After trying to live his life in this way, Enskog came to realise that it made neither him nor anyone round him any happier.
- His advisor was Gustaf Granqvist (1866-1922), an experimental physicist specialising in the physics of the electric arc, and Enskog chose the experimental study of gas diffusion as the topic for his research.
- He decided to become a schoolteacher but he was able to undertake a probationary year in Stockholm as well as fitting in a visit to Göttingen in Germany where he attended lectures by David Hilbert in the academic year 1912-13.
- Having completed his training as a schoolteacher, Enskog obtained an appointment as a temporary teacher of mathematics and physics at the gymnasium in the small town of Skövde.
- Over the next years Enskog combined working as a teacher while spending all his spare time undertaking research for his doctorate.
- By 1915 Enskog had largely completed the work for his thesis and sent his results to Oseen for comments.
- However, Oseen thought that Enskog's mathematical proofs lacked rigour.
- Enskog submitted his thesis Kinetische Theorie der Vorgänge in mässig verdünnten Gasen Ⓣ(Kinetic theory of processes in moderately dilute gases) to Uppsala University which was examined on 14 April 1917.
- There was still a problem in that Enskog had failed to prove that his series converged.
- Enskog's thesis studied the Maxwell-Boltzmann equations.
- Enskog began to work on this equation for his master's degree at Uppsala and made a remarkable prediction.
- However Enskog predicted it in a paper written in 1911.
- Enskog used Hilbert's methods to work out a series expansion of the velocity distribution function f and wrote this up for his doctoral dissertation at Uppsala in 1917.
- However Enskog made an important advance in 1921, although it described the rather artificial situation treating molecules as hard spheres.
- Chapman, who was still working on the Maxwell-Boltzmann equations, immediately saw the importance of Enskog's methods and developed them further.
- The book S Chapman and T G Cowling, The Mathematical Theory of Non-uniform Gases (1939) (which the authors dedicated to David Enskog) is the classic text on the modern kinetic theory of gases based on the approach by Enskog and Chapman.
- Enskog was unaware of Chapman's paper of 1916 when his Dissertation was published.
- Although the advent of quantum theory was to lessen the impact of this Chapman-Enskog theory, it was later seen to be still important in the new context.
- The research that Enskog conducted in the 1920s was done while he worked as a senior master at the grammar school.
- He had been awarded a scholarship for 1922-23 which had funded a trip to Göttingen and Munich in Germany where he attended lectures by Niels Bohr, David Hilbert, Arnold Sommerfeld, Richard Courant and Max Born.
- Reports on the candidates for the professorship at the Royal Institute of Technology were published making it appear unlikely that Enskog would be appointed as he was criticised for not having any university teaching experience.
- Chapman, however, attended a conference in Stockholm in August 1930 and met Enskog for the first time, although they had corresponded since 1917.
- The letter changed the outcome and later in 1930 Enskog was appointed professor of mathematics and mechanics at the Royal Institute of Technology in Stockholm.
- This was Enskog's first and last meeting as a member of this august body.
- Three days later, riding on a tram to a lecture at the Royal Institute of Technology, Enskog felt unwell.

Born 22 April 1884, Västra Ämtervik, Värmland, Sweden. Died 1 June 1947, Stockholm, Sweden.

View full biography at MacTutor

Origin Sweden

**O’Connor, John J; Robertson, Edmund F**: MacTutor History of Mathematics Archive