Johannes Robert Rydberg was interested in the debate concerning spectra and started his studies on the relations existing among the spectral lines long before Balmer published his formula. Independently from Rydberg, in 1890, two well known spectroscopists, Heinrich Kayser and Carl Runge tried to establish some general mathematical equations concerning the laws that govern spectroscopy and suggested solutions which were discussed with bright polemics, until the point of view of Rydberg prevailed, reaching the greatest recognition. The study of the composition of light emitted by incandescent bodies is the subject of spectroscopy. This discipline was born in 19th century and has played a fundamental role in the study of light emission and of the structure of atoms, and is an indispensable tool for understanding the working principles of masers or lasers. According to the H A Lorentz theory, light is emitted by atomic charged particles whose motion is influenced by the magnetic field according to the laws of classical electromagnetism.