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Wilhelm Eduard Weber was German physicist who studied magnetism and electricity. Working with mathematician Karl Gauss, he made sensitive magnetometers to measure magnetic fields, and instruments to measure direct and alternating currents. He also built an electric telegraph. The SI unit of magnetic flux, the weber, is named after him.
Weber defined an electromagnetic unit for electric current which was applied to measurements of current made by the deflection of the magnetic needle of a galvanometer. In 1846, he developed the electrodynamometer, in which a current causes a coil suspended within another coil to turn when a current is passed through both. In 1852, Weber defined the absolute unit of electrical resistance.
Wilhelm Eduard Weber was born on October 24, 1804, in Wittenberg, Germany (about 60 miles southwest of Berlin), in a family of 12 children. Weber was the son of Michael Weber who was a professor of divinity. The family Weber lived in the Languth House on the Schlossstrasse. Today the house is better known as “the house with the golden globe".
Languth House as it appears today
William was the second of three brothers. Two of his brothers, Ernst Heinrich Weber and Eduard Friedrich Weber, became noted scientists worked in anatomy and physiology. In 1815, after the Universities Halle and Wittenberg were merged, Wilhelm’s father Michael moved his family to Halle. William had received his first lessons from his father, but was now sent to the Orphan Asylum and Grammar School at Halle. Then Wilhelm attended the Francke Institute and the University.
Wilhelm Weber entered the University of Halle in 1822 where he studied physics and wrote his doctoral dissertation (Ph.D.) in 1826 on the acoustic theory of reed organ pipes. He remained teaching at Halle until 1831 when he was made professor of physics at Gottingen on the recommendation of the mathematician Karl Friedrich Gauss.
At Gottingen, Weber built a 3-km telegraph to connect the physics laboratory with the astronomical observatory where Gauss worked, and this was the first practical telegraph to operate anywhere in the world. Wilhelm Eduard Weber together with his friend Gauss investigated terrestrial magnetism. Gauss and Weber organized a network of observation stations in 1836-41 to correlate measurements of terrestrial magnetism made around the world.
The marble board (inscription: “First electrical telegraph") is fixed at the front wall of the observatory
During the time that Weber worked with Gauss on measuring magnetic strength he developed sensitive magnetometers and other magnetic instruments. This picture shows a portable magnetometer built by Wilhelm Weber in 1839.
Wilhelm Weber was Gauss-s assistant and leading experimental collaborator when he started working on the experimental validation of the Ampere force. He accomplished this research over the period 1832-1846. Weber-s discovery made a revolution in physics, the full implications of which are still unrealized. Worse, today, the underlying discovery itself is almost buried.
Ampere’s experimental conclusions drew on a series of brilliant geometrical deductions, derived from the observation of configurations of current-carrying wires in which the forces, presumably, cancelled each other, producing no observable motion. To validate the Ampere Law, one needed to be absolutely sure that the lack of motion was not due to friction in the joints of the apparatus, or related effects. Gauss and his young assistant, Wilhelm Weber, devised a new apparatus, the electrodynamometer, which could directly measure, to within fractions of a second of arc, the angular displacement produced in a multiply wound electric coil by another electrical coil perpendicular to it. By reducing the effects of each of the two coils to that of circular current loops, Ampere’s simple law for the force exerted by a current loop could be applied. Placing the coils in different positions, and at different distances from each other, allowed for determinations of the electrodynamic force, geometrically equivalent to those which Ampere had deduced form his null experiments.
Weber improved the tangent galvanometer invented by Hermann von Helmholtz and built an electrodynamometer suitable for studying the force produced by one electric current on another: when the same current passes through two concentric coils placed at right angles to each other, the resulting torque depends on the square of the current. The picture shows the electrodynamometer constructed in 1841 by Wilhelm Weber and used in the final determination of the validity of Ampere’s electrodynamics. It consists of two perpendicular electrical coils.
The outer coil is suspended in such a way that its rotation, under the influence of the inner coil, can be precisely determined by observing the deflection of the mirror image of a meter stick in a telescope, as in the Gauss-designed magnetometer. The inner coil can be removed, and placed at various distances.
This electrodynamometer was designed by Wilhelm Weber in 1845. In this electrodynamometer the magnetic field is provided by a current carrying coil instead of a permanent magnet. The instrument is operated in the null mode, i.e., the fiber suspending the rotating coil is turned so as to bring the coil back to its rest position, the current then being read from the angle of rotation of the fiber.
This was a secondary standard for current measurement until the 1920s when it was replaced by the more convenient direct reading meter patented by Edward Weston. (Reference: John T. Stock and Denys Vaughn, The Development of Instruments to Measure Current, Science Museum, 1983, p.39-40.)
When Victoria became Queen of Britain in 1837 her uncle became ruler of Hanover and revoked the liberal constitution. Weber was one of 7 professors at Gottingen to sign a protest and all were dismissed. The results of a rigorous program of instrument building and experimentation was interrupted by Weber’s expulsion from Gottingen University as a result of the political events of 1837.
He remained at Gottingen without a position until 1843 when he became professor of physics at Leipzig. His the most important scientific results were finally published at Leipzig in 1846 in his book “Elektrodynamische Massenbestimmungen” (Electrodynamical Measurements, 1846). These results completely confirmed the deductions of Ampere, and also introduced a new physical principle.
Wilhelm Eduard Weber, lithograph printed by Rudolf Hoffmann, ca. 1840, from the original artist Goettingen Petri
The discovery of the phenomena of electrical and magnetic induction had introduced a new element into the considerations of electrical law, not taken up in Ampere’s 1826 work. There thus existed, side by side, three seemingly valid descriptions of the electrical interaction: (1) the Coulomb-Poisson law, describing the interaction of two electrical masses at rest; (2) the Ampere law, describing the interaction of elements of moving electricity, and: (3) a description of the laws of induction, elaborated by Emil Lenz and Franz Neumann. In his Fundamental Electrical Law, stated in 1846, Weber achieved the unification of these various phenomena under a single conception.
Instead of the mathematical entities, described as current elements by Ampere, Weber hypothesized the existence within the conductor of positive and negative electrical particles. He assumed that the presence of an electrical tension caused these particles to move at equal velocities in opposite directions. If one regards an Ampere current element as containing, at any given instant, a positive and a negative electrical particle, passing each other, then in the pairwise relationship of two current elements, there are four interactions to be considered. By the Coulomb law, these interactions, consisting of two repulsions and two attractions, cancel each other.
However, the elementary experiments of Ampere had shown that a motion is produced between the wires, implying the existence of a force not described by the Coulomb law. For example, two parallel conducting wires attract each other when the current in the two wires flows in the same direction, and repel each other when the opposite is the case. The situation is perfectly well explained under the Ampere force law, when one takes into account the angular relationship of the respective current elements. However, Weber’s unifying approach was to assume that the relative velocities of the electrical particles produced a modification in the Coulomb electrostatic force, to produce the resultant force between the wires.
Considering all the configurations which Ampere had examined, as well as those arising from the phenomena of induction, he was able to formulate a general statement of the Fundamental Electrical Law. This showed that the general law describing the force of interaction of two electrical particles, depends upon the relative velocities and the relative accelerations of the particles. The Coulomb electrostatic law thus becomes a special case of Weber’s general law, when the particles are at relative rest.
In the Weber Electrical Law, there is a relative velocity, corresponding to the constant c in his formula, at which the force between a pair of electrical particles becomes zero. The Weber-Kohlrausch experiment, carried out at Gottingen in 1854, was designed to determine this value. It was found to be experimentally equal, in electrodynamic units, to the product of the velocity of light, in vacuo, with the square root of 2. That value, became known as the Weber constant.
In electromagnetic units, it was equal to the light velocity. Bernhard Riemann, who participated in the experiment, soon wrote up the obvious conclusion of a deep connection between light and electrodynamic, or electromagnetic phenomena. Unfortunately, Weber failed to take any notice of this fact. However, this unexpected link between electricity and optics became central to James Clerk Maxwell’s great development of electromagnetic field theory.
Wilhelm Eduard Weber
Another Weber’s important result was the development of a system of units that expressed electrical concepts in terms of mass, length, and time. Gauss had previously done this for magnetism. Since force was expressed in these dimensions, he was then able to find his law of electric force. The principle was not very satisfactory because it did not conserve energy, but with it Weber publicized the view that matter was made up of charged particles held together by the force.
Weber modified the central force concepts which pervaded physics in his book “Elektrodynamische Massenbestimmungen” (Electrodynamical Measurements, 1846) by presenting a force law which was dependent on velocity and acceleration. Weber also linked the force between atoms to the their potential energy. His work inspired the direction that physics took in the latter half of the century. The units of Gauss and Weber were adopted at an international conference in Paris in 1881. The unit of magnetic flux (the weber) is named in his honor.
Wilhelm Weber and Karl Friedrich Gauss; painter: Karl-Conrad-Friedrich Bauer
The SI unit of magnetic flux, weber (Wb), honors the German physicist Wilhelm Eduard Weber, one of the early researchers of magnetism. “Flux” is the rate (per unit of time) in which something crosses a surface perpendicular to the flow. If the something is a magnetic field, then the magnetic flux across a perpendicular surface is the product of the magnetic flux density, in teslas, and the surface area, in square meters. If a varying magnetic field passes perpendicularly through a circular loop of conducting material, the variation in the field induces a electric potential in the loop.
If the flux is changing at a uniform rate of one weber per second, the induced potential is one volt. This means that numerically the flux in webers is equal to the potential, in volts, that would be created by collapsing the field uniformly to zero in one second. One weber is the flux induced in this way by a current varying at the uniform rate of one ampere per second. The weber is a large unit, equal to 108 maxwells, and practical fluxes are usually fractions of one weber. (Because of this, when we want to induce an electric potential in a conductor with a changing field, as we do in all electric generators, transformers and electric motors, we loop the conductor into hundreds of coils, thus adding together the small voltages induced in each loop by the changing field.)
Wilhelm Weber’s brothers.
When Wilhelm Weber came to work at the Leipzig University, he often collaborated with his brothers Ernst and Eduard, renowned physiologists, that were already on the faculty. Actually, his collaboration with the brothers was started much earlier. Young Wilhelm Weber, just 18 years old at the time, assisted his brother Ernst in pioneering investigations on wave motion.
Their sophisticated research resulted in the publication in 1825 of “Wellenlehre, auf Experimenten gegrundet", a 575-page monograph on wave theory that included 18 copper plate illustrations. This classic book included the first detailed application of hydrodynamic principles to the study of the circulation of the blood. In 1833 Wilhelm Weber investigated the mechanism of walking together with his brother Eduard.
Ernst Heinrich Weber (1795-1878), right, and Eduard Friedrich Wilhelm Weber (1806-1871), left
In 1849 Wilhelm Weber returned to his post in Gottingen and, in 1855, he and Dirichlet became temporary directors of the astronomical observatory there. Weber’s later years at Gottingen were devoted to work in electrodynamics and the electrical structure of matter. Weber put forward in 1871 the view that atoms contain positive charges that are surrounded by rotating negative particles and that the application of an electric potential to a conductor causes the negative particles to migrate from one atom to another. He also provided similar explanations of thermal conduction and thermoelectricity.
Wilhelm Eduard Weber
Wilhelm Weber was described by Thomas Hirst in the following way: “He speaks and stutters on unceasingly, one has nothing to do but listen. Sometimes he laughs for no earthly reason, and one feels sorry at being not able to join him.”
Wilhelm Weber received many honours from England, France, and Germany, among which were the title of Geheimrat (privy councillor) and the Copley Medal of the Royal Society. Many of his extensive articles are in the six volumes of Resultate aus den Beobachtungen des magnetischen Vereins (1837-43), edited by himself and Gauss. Long term friendship and fruitful scientific collaboration of Weber and Gauss at the Gottingen University is memorized in this monument.
Monument of Gauss and Weber (standing) in Gottingen
Wilhelm Weber died on June 23, 1891 in Gottingen where he was buried.
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