Friedrich Paschen (22.01.1865-25.02.1947) was a German experimental physicist and a member of the Berlin Academy of Sciences (1925). He was born in Schwerin. He studied at the universities of Strasbourg and Berlin, and in 1888 received his doctorate at the latter. In 1888—91 he was assistant at the Academy in Münster, and in 1891 — 1901 at the Physical Institute of the Higher Technical School in Hanover. From 1901 he was professor at the University of Tübingen and director of the Physical Institute, and in 1924— 33 director of the Imperial Physico-Technical Institute (Berlin — Charlottenburg).
His work concerned atomic spectroscopy and the quantum theory of radiation. He made precision measurements of the wavelengths of many spectral lines, made a number of new light sources with the most varied kinds of excitation, carried out the most exact measurements of the dispersion of the substances used to make the refracting prisms of spectrometers, and detected many fine details in the structure of spectra. Together with C. Runge he studied (1895) the spectrum of the newly discovered helium. In 1889 he established the expression for the breakdown (striking) potential of an electric discharge in gases (Paschen's law). In 1908 he detected the first two lines of a new series of hydrogen in the infrared region of the spectrum (the Paschen series). In 1912, together with E. Back, he discovered the effect of the simplification of the splitting pattern of spectral lines in a strong magnetic field (the Paschen — Back effect). He studied the fine structure of the helium lines (1916), thereby confirming the theoretical predictions of A. Sommerfeld, and the complex spectrum of neon (1920). He designed a large number of measuring instruments, in particular a highly sensitive radiomicrometer and galvanometer and a concave diffraction grating.
He created a school of spectroscopists (E. Back, W. Gerlach, A. Landé, H. Schüler and others). A foreign member of the USSR Academy of Sciences (1930).