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1820 __ Production of electricity from magnetism — The Ether versus Action at a Distance
Hans Christian Ørsted (Oersted) (1777-1851), Michael Faraday (1791-1867)
Comment : In 1820, a Danish scientist Hans Christian Oersted had discovered that the passage of an electric current through a wire could deflect a magnetic needle suspended nearby. He had observed that the "electrical conflict" was not confined to the conductor but was dispersed quite widely in the surrounding space, and the forces of this conflict acted in circles around the wire. The announcement of this discovery caused a sensation throughout the scientific world, particularly as it shattered Newtonian theories that forces only act along straight lines between two points. Michael Faraday·s work was fundamental to the development of electromagnetic field theory, and to the exploitation of electromagnetic waves.1831: The English experimental genius Michael Faraday discovered how to produce electricity from magnetism.1832: Faraday proposed that magnetic action and electric induction are progressive and require time for their transmission he likened them to vibrations on the surface of disturbed water.Without Faraday, the achievements of Maxwell, Hertz, Lodge, Popov, Marconi and others would never have taken place, and the introduction of radio broadcasting would have been delayed by many years. During the course of his experiments, Faraday had observed that an appreciable element of time was required in order to transmit a magnetic force. Similarly, he surmised that charges due to static electricity would also require time to transmit. Pursuing these ideas further, he speculated that electric and magnetic forces were propagated by some form of wave motion, rather like "the vibrations upon the surface of disturbed water". ("Six Great Pioneers of Wireless", EBU Technical Review Spring 1995, pp. 82-96)The Ether versus Action at a Distance.From the sixteenth century onwards, arguments had been raging over how the phenomenas of gravitation, light and heat were physically transmitted through empty space. In the early seventeenth century, it is broadly true to say that the theories of René Descartes (1596-1650) were widely accepted. Descartes and his followers (who were known as Cartesians) believed that bodies can only act upon each other by direct pressure or impact. They assumed that space was filled with a medium called the ether which, although imperceptible to human senses, was nevertheless capable of transmitting forces, such as heat and light, and exerting effects upon material bodies that were immersed in it. The ether was thought to consist of particles which were continuously in motion, which enabled it to perform its mysterious functions. These theories were gradually overturned by the work of Isaac Newton (1642-1727), whose theory of universal gravitation was published in 1687. Newton proposed that all bodies attract one another with a force which is proportional to the product of their masses and inversely proportional to the square of the distance between them. Although he did not seem to realize it, Newton was in fact rejecting the Cartesian concept of an ether in favour of accepting the theory of action at a distance. Initially, Newton·s laws of gravitation were not accepted by many, as they seemed to violate the accepted philosophical principle of the time "that matter cannot act where it is not". Philosophers on the Continent of Europe were particularly slow to adopt this principle and it was not until the end of the eighteenth century that Newton·s ideas had come to be accepted. By then, the idea of action at a distance had become so firmly established that the mere idea of gravitational, electrical or magnetic forces requiring a medium such as the ether for their propagation seemed almost as absurd as action at a distance had seemed a century earlier. However, when Michael Faraday arrived on the scene in the early nineteenth century, he was almost alone in rejecting the ideas of action at a distance. Although Faraday may not have understood how forces could be transmitted through a medium and, indeed, what such a medium might consist of, he was firmly convinced that magnetic and electric forces did act in some form of a medium a view held some years later by James Clerk Maxwell who brought about the final rejection of action at a distance. ("Six Great Pioneers of Wireless", EBU Technical Review Spring 1995, pp. 82-96)
French comment : Hans Christian Ørsted (14 août 1777 à Rudkøbing – 9 mars 1851 à Copenhague) fut un physicien et un chimiste danois. Il est à l'origine de la découverte de l'interaction entre électricité et magnétisme. En avril 1820, lors d'un cours sur l'électricité qu'il faisait à ses étudiants, il découvrit la relation entre l'électricité et le magnétisme dans une expérience qui nous apparaît aujourd'hui comme très simple. Il démontra, par l'expérience, qu'un fil transportant du courant était capable de faire bouger l'aiguille aimantée d'une boussole. Il pouvait donc y avoir interaction entre les forces électriques d'une part et les forces magnétiques d'autre part, ce qui était révolutionnaire pour l'époque. Ørsted ne suggéra aucune explication satisfaisante du phénomène, ni n'essaya de représenter le phénomène dans un cadre mathématique. Il publia cependant le 21 juillet 1820 ses résultats expérimentaux dans un article de 4 pages en latin intitulé : "Experimenta circa effectum conflictus electrici in acum magneticam". Ses écrits furent traduits et diffusés dans l'ensemble des communautés scientifiques européennes et ses résultats vivement critiqués. Ampère prit connaissance de ses résultats en septembre 1820 et développa rapidement la théorie qui allait permettre l'émergence de l'électromagnétisme. Le succès de cette théorie contribua à la reconnaissance d'Ørsted, aussi bien dans la communauté scientifique que parmi ses concitoyens. (Compiled from various sources)
Urls : https://www.ebu.biz/fr/technical/trev/trev_263-pioneers.pdf (last visited ) http://www.ampere.cnrs.fr/parcourspedagogique/zoom/oersted/index.php (last visited )

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