Traveling with the Atom

Allegheny College


(compiled by Dr.Glen E. Rodgers)

A photograph of Thomson's cathode ray tube showing the embedded electric plates that he used to divert the ray that found was composed of a beam of negatively charged electrons
Thomson working with his cathode ray tube.
© Science Museum/Science & Society Picture Library
J. J. Thomson
English Physicist
(1856 - 1940)
Contribution to the Development of the Atomic Concept
Thomson, working at the Cavendish Laboratory of Physics in Cambridge, determined in 1897 that cathode rays were beams of electrons.  He also determined the mass to charge ratio of an electron by balancing the effect of electric and magnetic fields on these cathode rays.  He proposed the "plum-pudding" model of the atom in which thousands of electrons were embedded in a massless cloud of electricity.  Later he argued that the number of electrons in an atom was approximately equal to the atomic weight of that element.  He was awarded the 1906 Nobel Prize in Physics.

Web Sources of Biographical Information
The Discovery of the Electron
Science Museum (London)
Nobel Prize Webpage on Thomson
Interactive animation of the e/m experiment (The Science Museum)
The Thomson Experiment
Atom: the Incredible World

Some Teaching Links
Figure of Thomson and his tube showing that cathode rays cast a shadow Adapted from Figure VII-1, Biography of Physics, George Gamow, p 212
Cathode Ray Animation
The Science Museum, London
Selected Biographical Books, Sections of Books, and Articles
Full biographical information on Sacks' book Uncle Tungsten p 244; 288
Full biographical information on Asimov's Biographical Encyclopedia of Science and Technology, 2nd Ed. pp 561-563
Thomson's 1897 paper on cathode rays The Cavendish Laboratory, 1874-1974, J. G. Crowther, Science History Publications, New York (1974).  (Sometimes out of print but perhaps available from
Leadership and Creativity - A History of the Cavendish Laboratory, 1871-1919 (ARCHIMEDES Volume 5) New Studies in the History and Philosophy of Science, by Dong Won Kim (scheduled to be available March, 2002)

Some Scientific/Historical Traveling Sites
The Cavendish Laboratory of Physics.  The "old Cavendish" was (on Free School Lane) but it now houses other departments (1,2,3) Free School Lane (near King's College) in Cambridge, England.  A plaque* explaining the electron was discovered here by Thomson is still available
The Museum at the Cavendish Laboratory.  A small but wonderfully engaging museum on the first floor of the Bragg building has a number of exhibits including Thomson's original e/m tube and biographical information* (1,2,3) The Cavendish Laboratory
Madingley Road
Cambridge, England
(Need to make arrangements in advance to see the small museum.)
* see following Rodgers link to scientific/historical sites for further information.
(1) Taken from The Scientific Traveler, Charles Tanford and Jacqueline, John Wiley & Sons, NY (1992).
(2) Taken from A Travel Guide to Scientific Sites of the British Isles, Charles Tanford and Jacqueline Reynolds, John Wiley & Sons, NY (1995).
(3) Taken from Guide of Eurpoean Museums with collections on History of Chemistry, compiled by Jan W. van Spronsen, Federation of European Societies, Antwerp (1996)

Link to Dr. Rodgers' Scientific/Historical Site on the Cavendish Laboratory.

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