PLUCKER, JULIUS

born June 16, 1801, Elberfeld, Duchy of Berg died May 22, 1868, Bonn German mathematician and physicist whose work suggested the far-reaching principle of duality, which states the equivalence of certain related types of theorems. He also discovered that cathode rays (electron rays produced in a vacuum) are diverted from their path by a magnetic field. This effect is a principle vital to the development of modern electronic devices, such as television. Plcker attended the universities of Heidelberg, Berlin, and Paris. In 1829, after four years as an unsalaried lecturer, he became extraordinary professor at the University of Bonn. From his lectures came his first great work, Analytisch-geometrische Entwicklungen, 2 vol. (182831; The Development of Analytic Geometry), in which he introduced the abridged notation in analytic geometry. In 1829 Plcker proposed a revolutionary idea in analytic geometry: that the fundamental geometric element need not be the point but could be the straight line. Through this idea he developed the principle of duality. In 1834 Plcker became professor of mathematics at the University of Halle and two years later professor of mathematics at the University of Bonn. Theorie der algebraischen Curven (1839; Theory of Algebraic Curves), his greatest work, contains equations detailing the number of singularities (points at which there is no unique tangent line) on algebraic curves, and his System der analytischen Geometrie (1835; System of Analytic Geometry) introduced the use of linear functions in place of the usual coordinate points. Plcker's System der Geometrie des Raumes in neuer analytischer Behandlungsweise (1846; System of the Geometry of Space in a New Analytical Treatment) contains a more systematic and polished rendering of his earlier results. After his appointment as professor of physics at Bonn in 1847, Plcker began research on the behaviour of crystals in a magnetic field and then studied the properties of magnetic bodies, establishing results integral to knowledge of magnetism. He discovered and investigated the magnetic deflection of cathode rays and thus stimulated research in electronics and atomic physics. At first alone and later with the German physicist Johann W. Hittorf, Plcker made many important discoveries in spectroscopy. He anticipated Robert Bunsen and Gustav R. Kirchhoff, both of Germany, in announcing that spectral lines were characteristic for each chemical substance and in indicating the value of this discovery to chemical analysis. According to Hittorf, Plcker was the first who saw the three lines of the hydrogen spectrum that a few months after his death were recognized in the spectrum of the solar prominences, thus solving a mystery of modern astronomy. In 1862 he pointed out that the same element may exhibit different spectra at different temperatures. In 1865 he returned to the study of mathematics and later published his work on modern pure geometry of space, Neue Geometrie des Raumes gegrndet auf die Betrachtung der geraden Linie als Raumelement (186869; New Geometry of Space Founded on the Treatment of the Straight Line as Space Element).