Johannes Rydberg , who died #OTD in 1919, was a Swedish physicist mainly known for devising the Rydberg formula, in 1888, which is used to describe the wavelengths of photons (of visible light and other electromagnetic radiation) emitted by changes in the energy level of an electron in a hydrogen atom.
https://en.wikipedia.org/wiki/Johannes_Rydberg
"As I have pointed out already in my general exposition of the constitution of line spectra, and have afterwards tried further to confirm, there can be no doubt that these series are really parts of a single group of lines with two variable integral parameters, the general formula of which can be written approximately."
Lines in the Hydrogen Spectrum (1897)
~Johannes Rydberg (8 November 1854 – 28 December 1919)
