Julius Plücker (16.07.1801-22.05.1868) — a German mathematician and physicist. He was born in Elberfeld. In 1824 he received the degree of Doctor of Philosophy at the University of Marburg. In 1825-28 he was an assistant, in 1828-33 and 1836—68 professor at the University of Bonn (in 1834—36 professor at the University of Halle).
His work in physics concerned the study of magnetism, electric discharges in gases, the action of a magnetic field on these discharges, the spectra of gases, and cathode rays. He constructed (1855) tubes for studying the spectra of gases, established (1859) that the spectrum of an electric gas discharge characterises the nature of the gas, detected the first three lines in the spectrum of hydrogen, and studied the fluorescence of the glass of the tube in which the discharge takes place. In 1859 he discovered cathode rays and observed their deflection under the action of a magnet. He studied (1861) the spectra of hydrogen, oxygen, iodine and nitrogen and introduced (1865) the division of spectra into line spectra and band spectra. With H. Geissler he constructed a standard thermometer. In 1847 he discovered the magnetic properties of tourmaline crystals and, independently of M. Faraday, the paramagnetism of oxygen.
The Copley Medal (1868).