J.J. Thomson's positive ray apparatus, replica of Cavendish Lab apparatus
date: label: Date made
content: ca. 1960 (original 1907-1912)
name: label: manufacturer
content: University of Cambridge. Department of Physics. Cavendish Laboratory
notes: label: Description
content: J.J. Thomson's positive ray apparatus, replica of Cavendish Lab apparatus. Object ID EM.N-08014; Overall length 62 cm x width 35 x height 44 cm.
label: Description
content: Object is a replica of the original which resides at Cavendish Laboratory, Cambridge University, England. Wood base supports, at one end, a horizontal glass discharge tube attached to a chamber fitted between the poles of an electromagnet. The chamber contains a pair of plates for deflection of the beam of "positive rays" (ions) passing through from the discharge tube. The rays fall on a phosphorescent screen at the other end of the apparatus, where a photographic plate can also be positioned.
label: Description
content: Basic Principle
label: Description
content: Thomson's positive ray apparatus were analogous to his cathode-ray tubes (see objects EM.N-08013A and EM.N-08013B); in that they measured the ratio of charge to mass of "positive rays" instead of electrons (cathode rays).
label: Description
content: Ions, created by an electric discharge in the glass bulb, are accelerated towards its mouth. This beam of "positive rays" is then deflected vertically by a magnetic field and horizontally by an electric field, forming a parabolic trace on a phosphorescent screen—all atoms or molecules of the same charge-to-mass ratio falling along one parabola. This object is a replica of the fourth such apparatus Thomson constructed. With it, the traces were recorded photographically for the first time. For a concise review of J.J. Thomson, the Cavendish Laboratory, and Thomson's cathode ray tube and positive ray apparatus, see J .J. Thomson - the Centenary of His Discovery of the Electron and his invention of Mass Spectrometry, Rapid Communications in Mass Spectrometry, Vol.11, 2-16 (1997).
label: Location
content: Currently not on view
place: label: place made
content: United Kingdom: England, Cambridge
label: Associated Place
content: United Kingdom: England, Cambridge
topic: label: general subject association
content: Science & Scientific Instruments
label: general subject association
content: Modern Physics
setName: label: See more items in
content: Medicine and Science: Modern Physics
label: See more items in
content: Science & Mathematics
creditLine: label: Credit Line
content: Cavendish Laboratory
dataSource: label: Data Source
content: National Museum of American History
identifier: label: ID Number
content: EM.N-08014
label: accession number
content: 224580
objectType: label: Object Name
content: Positive Ray Apparatus (replica)
label: Object Name
content: positive ray apparatus (replica)
label: Object Name
content: positive ray apparatus (replica)
label: Object Name
content: Electron Tube, Positive Ray Apparatus
physicalDescription: label: Physical Description
content: wood; glass; metal (overall material)
label: Measurements
content: overall: 44 cm x 35 cm x 62 cm; 17 5/16 in x 13 25/32 in x 24 13/32 in