On 10th May, 2022, the old Physics Department of Lund University, Sweden, was inaugurated as an EPS Historic Site. The building, which is located at Biskopsgatan 3, Lund, served the Lund physicists during the years 1885 to 1950. It had two halls for instruments, an auditorium, 12 offices, a library and a workshop. The building then became the base for classical studies (Classicum) until in 2009 after renovation became the site of the interdisciplinary Pufendorf Institute of Advanced Studies. The ceremony was actually planned for 26th May 2020, but had on short notice to be moved forward due to the Covid-19 pandemic.

The nomination as an EPS Historic Site is based on the work of Johannes (Janne) Rydberg (1854-1919), who was active in analyzing atomic spectral lines, which Bunsen and Kirchhoff around 1850 had found to be specific for each species. Balmer had in 1885 found a formula to describe the lines of hydrogen. Being an excellent mathematician, with a great feeling for numbers, Rydberg found a more general formula, which also worked well, e.g. for the alkali atoms. He presented his first results in 1887 in a report to the Royal Swedish Academy of Sciences, and more in detail in a presentation to the Mathematical-Physical Society in Lund in 1888. The full account of his findings occurs in a scientific article published in German in 1890 (Zeitschrift für Physikalische Chemie). The most amazing aspect of this formula was that there occurred a constant, which was the same for all elements and all spectral series. In his early model for the atomic structure, Niels Bohr could in 1913 also give a theoretical value for the constant, which well agreed with the experimental value found by Rydberg. The constant came to be known as the Rydberg constant, and is presently determined to an extremely high precision using laser spectroscopy. Rydberg´s name is also associated with the much studied Rydberg atoms, which are very highly excited atoms becoming accessible through laser spectroscopy, and through the Rydberg-Ritz combination principle of atomic spectroscopy.

It can be noted that Manne Siegbahn (1886-1978) was also active in the building, making ground-breaking precision X-ray spectroscopy studies. Bengt Edlén (1906-1993), who in 1941 solved the old problem of the origin of the corona lines from the sun, was a further prominent Lund atomic physicist.

The inauguration ceremony was organized and led by Sune Svanberg, who had also made the site nomination. Stacey Ristinmaa Sörensen, the Pufendorf Institute director, welcomed a large crowd of fellow physicists assembled to celebrate, and Joachim Schnadt, chairman of the Department of Physics, recalled the work by Rydberg. Mats Helmfrid expressed his appreciation on behalf of the Lund City Council. The chairman of the EPS selection committee for historic sites, Karl Grandin, introduced the EPS programme together with the EPS president, Luc Bergé, who also performed the solemn uncovering of the memorial plaque, accompanied by a brass band.

A Rydberg Lecture, in a series of named lectures sponsored by the Royal Academy of Science, followed at the new Physics Department directly after the inauguration ceremony. The speaker was Jun Ye, JILA, National Institute of Standards and Technology and University of Colorado, who in his talk “Tick Atoms in Unison” described how extremely accurate atomic clocks could be influenced by the gravitational shift due to only one mm of vertical clock movement.

A Rydberg dinner arranged with some 30 guests in the recognized building, with speeches including by the Lund University vice Chancellor, Erik Renström, concluded a memorable day.

The memorial plaque at the old Physics Department, Lund University, has just been uncovered.
FLTR: Sune Svanberg, Lund Laser Centre, Karl Grandin, Chair of the EPS Historic Sites Selection Committee,
Luc Bergé, EPS President, Joachim Schnadt, Department of Physics, and Mats Helmfrid, Lund City Council

Photos: Sune Svanberg & Katarina Svanberg