Background
Paul Drude was born on July 12, 1863 in Brunswick, Germany, into a Jewish family. He was the son of a medical doctor in Brunswick.
Drude studied at the University of Göttingen. His original ambition was to become a mathematician, and he studied mathematics, first at Göttingen and then at Freiburg and Berlin. In his sixth semester he returned to Göttingen, where he came under the influence of W. Voigt and as a result began to study theoretical physics.
Drude studied at the University of Göttingen. His original ambition was to become a mathematician, and he studied mathematics, first at Göttingen and then at Freiburg and Berlin. In his sixth semester he returned to Göttingen, where he came under the influence of W. Voigt and as a result began to study theoretical physics.
The Drude model electrons (blue) constantly bounce between heavier, stationary crystal ions (red).
In 1906, at the height of his career, Drude became a member of the Prussian Academy of Sciences.
Drude was a member of the Saxon Academy of Sciences from June 17, 1895 to April 1, 1900.
Demonstration of one of Drude's experiments.
A photo of Drude with his wife and children.
The crater Drude on the Moon is named after him.
Paul Drude was born on July 12, 1863 in Brunswick, Germany, into a Jewish family. He was the son of a medical doctor in Brunswick.
Drude attended the local Gymnasium and then went on to study at the University of Göttingen. His original ambition was to become a mathematician, and he studied mathematics, first at Göttingen and then at Freiburg and Berlin. In his sixth semester he returned to Göttingen, where he came under the influence of W. Voigt and as a result began to study theoretical physics.
Drude’s dissertation, under Voigt’s direction, was a purely theoretical treatment of the equations governing the reflection and refraction of light at the boundaries of absorbing crystals.
Drude worked with Voigt at Göttingen until 1894. He then moved to Leipzig where he pursued both theoretical and practical researches on the propagation of electromagnetic waves and wireless telegraphy, as well as continuing his work on physical optics. His interest in the physical determinants of optical constants led him toward an attempt to correlate and account for the optical, electrical, thermal, and chemical properties of substances.
Drude’s interest in these problems was stimulated by his own growing conviction, based on studies begun in 1888, that Maxwell’s electromagnetic theory was superior to the older mechanical view of light. This conviction led him to publish Physik des Äthers (1894), one of the first German books to base explanations of electrical and optical effects on Maxwell’s theory.
By 1898 Drude had begun to consider these matters within the structure of the theory of electrons; indeed, he thereby laid the foundation for understanding such phenomena as conduction in metals, thermal conductivity, and optical properties of metals as interactions of the electrical charges of substances with their environment.
With the death of Wiedemann in 1889, he assumed the editorship of Annalen der Physik, the most prestigious of physics journals. In 1901, shortly after the publication of his Lehrbuch der Optik, Drude moved to Giessen where he became director of the Institute of Physics.
In Giessen, where he remained until 1905, Drude continued his work in optics and the electron theory. Having declined other appointments, it was only with some reluctance that he answered the call to Berlin to take over directorship of the physics institute. Almost immediately after Drude assumed this position, the size of the institute’s stall' was enlarged by a third in order to meet the demands of the increase of both the theoretical and the practical work that he brought with him. He died suddenly and unexpectedly within a year of moving to Berlin. The cause of death was suicide.
Drude may be considered the intellectual descendant of Franz Neumann - the first of Germany’s great theoretical physicists, who developed a mechanical theory of light propagation based on the work of Fresnel and closely related to Fresnel’s own theory. Voigt, whose work continued that of Neumann, was particularly interested in magneto- and electro-optics. Drude’s dissertation was a direct offshoot of Voigt’s work. Voigt then set him the problem of checking his work in the laboratory, using crystals of bournonite.
The experimental difficulties were great, and Drude almost immediately realized that the optical constants of such crystals were not independent of the state of the crystal’s surface. He discovered that the index of refraction and the coefficient of reflection of a crystal changed steadily from the time it was freshly cleaved. With characteristic care and thoroughness Drude then undertook a reexamination of the optical constants of a wide variety of absorbing substances, making measurements as difficult and exacting as those of the original experiments. When he was finished the optical constants of a wide variety of substances were known to an accuracy hitherto unthinkable.
This work occupied Drude from 1887 to 1891. During this period, too, he first became interested in Maxwell’s work in electrodynamics, stimulated by Hertz’s detection of electromagnetic radiation. Maxwell’s treatise of 1873 was translated into German in 1882; but Maxwell’s views were not widely accepted. The mechanical view of light propagation still held sway, and it had been under the influence of that theory that Drude had been working.
In 1888 he began an intensive four-year study, first immersing himself in the electromagnetic point of view, then reexamining the mechanical theory of light. He did not feel obliged to reject the mechanical theory which - although it presented some difficulty, especially in regard to the propagation of transverse waves through an elastic medium - had served so well.
Finally Drude took a phenomenological approach, attempting to remove nonessential elements from the mechanical formulation of optics. He argued that the differential equations and the imposed boundary conditions must be retained while assumptions about the mechanical nature of light waves and the elasticity of the ether were extraneous. He published the fruits of his investigation in a paper entitled “In wie weit genügen die bisherigen Lichttheorien den Anforderungen der praktischen Physik?” (1892). In this paper Drude pointed out that if the investigator restricted himself to differential equations and necessary boundary conditions, which he designated as the “explanation system” (Erklärungssystem), the mechanical and electromagnetic theories were equivalent.
Drude gradually took up the electromagnetic view-point. In another paper of 1892, “Ueber magnetio-optische Erscheinungen,” he developed a system of equations directly from Maxwell’s equations to account for Kerr’s discovery that the reflectivity of magnetic substances (iron, cobalt, and nickel) is influenced by the state of magnetization and for Kundt’s observation that the plane of polarization of light is rotated in passing through thin plates of these substances.
Although the ease with which Maxwell’s theory allowed such work to be done was important to Drude, he did not yet advocate one theory to the exclusion of the other. Rather, for another two years he lectured at Gottingen on the Maxwell theory; these lectures led to the publication of his first book, Die Physik des Athers (1894). As a result of the heuristic effect that Maxwell’s theory had on his own work between 1894 and 1898, Drude became an advocate of the electromagnetic view.
With his move to Leipzig, Drude’s work on physical constants and his work on electromagnetic radiation began to merge into one set of coherent concerns. Drude had already hinted in some of his published work that by using the electromagnetic theory one might be able to explain electrical and optical properties of matter as the interaction of electromagnetic fields with electrical charges contained within the body. The publication of Lorentz’ electron theory between 1892 and 1895 undoubtedly spurred him in that direction.
Shortly after arriving at Leipzig in 1894, Drude undertook further investigations on the relationship between optical and electrical constants and the constitution of substances. Using seventy to eighty centimeters radiation, he measured coefficients of absorption in a wide variety of solutions and compared these to coefficients of conductivity for the same solutions. According to Maxwellian theory, a close correlation should have existed between electrical conductivity and absorption of light - the higher the conductivity, the greater should be the absorption. Drude found, however, that this was not always the case.
Drude was able to demonstrate that selective absorption of seventy-five centimeters radiation was directly related to the chemical structure of substances and that it was the hydroxyl radical (OH) that was responsible. Thus he developed a new practical analytic tool for chemists.
Drude did not make these researches serially; typically, he had several different research projects in progress at the same time - in addition to lecturing, directing doctoral students, heading the various physical institutes, and editing the Annalen der Physik. Drude carried this diverse and taxing load with grace and performed his duties with characteristic thoroughness.
The organization of Drude’s Lehrbuch der Optik (1900) reflects his own approach to problems in optics. The first half of the book is devoted almost exclusively to the phenomena and to their mathematical characterization. Then, after a brief outline of the mechanical and electromagnetic theories, Drude gives what he considers to be the advantages of the electromagnetic theory: first, transverse waves are a direct consequence of Maxwell’s conception of electromagnetic interaction; second, special boundary conditions are not required in the electromagnetic theory for radiation in the optical region of the spectrum; and third, the velocity of light can be determined directly from electromagnetic experiments.
Drude’s move to Giessen occurred at a time when he was intent on understanding the optical, thermal, and electrical properties of metals by application of the electron theory. Drude was not the only person interested in such a practical application of the electron theory. Both J. J. Thomson and E. Riecke made substantial though different contributions. In the theory developed by Drude every metal contains a large number of free electrons, which he treated as a gas, the electrons having an average kinetic energy equal to the average kinetic energy of the atoms and molecules of the substance. The essential difference between conductors and nonconductors was that nonconductors contained relatively few free electrons.
In early versions of his theory, Drude assumed that both positive and negative electrons were part of the “gas” but in a later simplification assumed that only negative electrons were mobile. Using the temperature of the substance as an index of the average kinetic energy of the particles in the electron gas, the velocity of the electrons should be enormous if it were not for the very small mean free path - due, mainly, to collisions with atomic centers.
Drude was an extraordinary member of the Saxon Academy of Sciences from June 17, 1895 to April 1, 1900. In 1906, at the height of his career, he became a member of the Prussian Academy of Sciences.
In 1894 Drude married Emilie Regelsberger, the daughter of a Göttingen jurist. The couple had four children.