Rydberg, Johannes Robert (1854-1919)

Swedish physicist who discovered a mathematical expression that gives the frequencies of spectral lines for elements. It includes a constant named the Rydberg constant after him. Rydberg was born in Halmstad and studied at Lund, where he spent his whole career, becoming professor 1897. Rydberg began by classifying spectral lines into three types: principal (strong, persistent lines), sharp (weaker but well-defined lines), and diffuse (broader lines). Each spectrum of an element consists of several series of these lines superimposed on each other. He then sought to find a mathematical relationship that would relate the frequencies of the lines in a particular series. In 1890, he achieved this by using a quantity called the wave number, which is the reciprocal of the wavelength. The formula expresses the wave number in terms of a constant common to all series (the Rydberg constant), two constants that are characteristic of the particular series, and an integer. The lines are then given by changing the value of the integer. Rydberg then went on to produce another formula, which would express the frequency of every line in every series of an element.