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Meet Janne Rydberg

The Rydberg Core Laboratory is named after the mathematician and physicist Johannes “Janne” Rydberg (1852–1919). He is mainly known for devising the famous Rydberg formula which is used to predict the wavelengths of the spectral lines of the elements. He is often referred to as the father of modern atomic spectroscopy.

Johannes Robert Rydberg, the father of modern atomic spectroscopy. Photographer: Per Bagge. Reproduction: Lund University Library.

The mathematician and physicist Johannes Robert (Janne) Rydberg was born in Halmstad in 1854. After final exams from Halmstads Högre Läroverk, he began studies at Lund University in 1873. Rydberg was appointed as assistant in physics at Lund University as early as 1876, although his interests at this stage were dominated by mathematics. Rydberg`s talent in mathematics led to his PhD on the construction of conical sections in 1879. After a second thesis on functional analysis in 1880, Rydberg was appointed as associate professor of mathematics.

Rydberg´s first article in physics was entitled: Studies on friction electricity, a study that led to his appointment as associate professor of physics at Lund University in 1882. His great interest in numerical patterns and regularities proved highly useful in his studies of the periodic table of the elements. Pioneering work carried out by Mendeleev showed a remarkable periodicity in the chemical and physical properties of the elements when they were arranged according to increasing atomic weight. The connection between the observed spectra of elements and their chemical properties had been studied previously in experiments by Meyer, Kirchhoff and Bunsen, but a theoretical explanation for their experimental findings had not been found. Rydberg pointed out that the periodic table of the elements clearly indicated that inter-atomic forces varied in accordance with the atomic weight, and that many chemical and physical properties derive from recurrent features in the structure of the atoms. He also argued that spectral analyses was the best tool for studying the structure of atoms and was therefore the best tool for unraveling the physics behind the periodic table of the elements. It was not until the advent of quantum mechanics in the 1920s that it was clarified that similarities in the chemical and physical properties of the elements reflect similarities in the valence shell of the atoms.

Due to the ever-increasing sophistication of experimental tools, accurate spectra were already accessible for many elements. The presence of line spectra had previously been noticed by Liveing and Dewar. In the famous article On the structure of line spectra of the chemical elements from 1890, Rydberg could describe all known spectral series with the formula:

Here σ is the wave number (reciprocal wavelength), R the so-called Rydberg constant, and m and n are integers, with n>m. Of these integers m has a definite value, while n may vary. The numbers a and b are known as quantum defects. It should be mentioned that Balmer a few years before had discovered a mathematical expression that described the spectral lines of hydrogen. His expression is a special case of the Rydberg formula, with m=2 and a=b=0.

In spite of the fact that Rydberg never found a deeper explanation for his formula (this was to be achieved by Niels Bohr), his contributions to modern physics can hardly be overestimated. For this reason Rydberg is often referred to as the father of modern atomic spectroscopy. Rydberg was appointed professor of physics at Lund University in 1901, a position that he retained until his death in 1919.

Updated 2018-12-20