Ruhmkorff electric machine
name: label: maker
content: Ruhmkorff, Heinrich Daniel
notes: label: Description (Brief)
content: An electrical generator having wooden base with four brass feet, two electromagnet coils, a brass knife switch, and a frame that supports a hand-cranked gearing mechanism and a copper disc armature. Etched on knife switch: "Ruhmkorff a Paris".
label: Description (Brief)
content: At the Academie des Sciences in Paris in September 1855, the French physicist, Leon Foucault (1819-1868), showed that a copper disc that rotates freely on its own is difficult to move when placed between the poles of an electromagnet and heated by what are now known as eddy currents. As word of this discovery spread throughout the scientific community, Foucault apparatus was available from Heinrich Daniel Ruhmkorff (1803-1877), a German artisan who worked in Paris and specialized in electrical instruments. The inscription on this example reads "Ruhmkorff a / Paris."
label: Description (Brief)
content: In 1858, the Smithsonian paid 300 Fr. to H. Bossange, its agent in Paris, for an "Appareil de Foucault pour chauffer un disque par le Magnetisme." Joseph Henry, the physicist who served as the founding Secretary of the Smithsonian, mentioned it in 1857. In his words: "A striking example of the transformation, as it were, of the force of motion into heat is exhibited by an article of apparatus now in the cabinet of the Smithsonian Institution and devised by M. Leon Foucault, of Paris. Between the poles of a strong electric-magnet a heavy metallic disc is made to rotate, and although the revolving body does not touch the magnet, yet its motion is stopped by it in a few seconds. The momentum of the disc which is thus overcome gives rise to heat; for the re-action of the magnet produces a current of electricity, and in the resistance to this the heat is generated. A body in motion is in a state of power, and it cannot come to rest without producing some effect on the surrounding matter. The ultimate effect in this case is an agitation of the atoms of the metal."
label: Description (Brief)
content: [Note: it's possible this unit is a replacement from after the 1865 Castle fire.]
label: Description (Brief)
content: References: Foucault, "De la Chaleur Produite par !'Influence de I' Aimant sur les Corps en Mouvement," in Leon Foucault, <i>Receuil des Travaux Scientifiques</i>, volume 1 (Paris, 1878), 342-344.
label: Description (Brief)
content: Joseph Henry, "Terrestrial Physics, and Temperature," (1857), reprinted in
label: Description (Brief)
content: <i>Scientific Writings of Joseph Henry</i>, volume 2 (Washington, 1886), 138.
label: Description (Brief)
content: J. Jamin, <i>Cours de Physique de l'Ecole Polytechnique</i>, volume 3 (Paris, 1869), 304.
label: Description (Brief)
content: A. Privat Deschanel, <i>Elementary Treatise on Natural Philosophy</i>, part 2, (New York, 1874), 447-450.
label: Location
content: Currently not on view
setName: label: See more items in
content: Work and Industry: Electricity
creditLine: label: Credit Line
content: From the Smithsonian Institution
dataSource: label: Data Source
content: National Museum of American History
identifier: label: ID Number
content: EM.181551
label: catalog number
content: 181551
label: accession number
content: 32407
objectType: label: Object Name
content: Electric Machine
label: Object Name
content: generator
physicalDescription: label: Measurements
content: overall w/ handle: 16 in x 15 13/32 in x 14 3/4 in; 40.64 cm x 39.116 cm x 37.465 cm