Sir Joseph John Thomson
Sir Joseph John Thomson, b. Dec. 18, 1856, d. Aug. 30, 1940, is
universally recognized as the British scientist who discovered
and identified the electron. At the age of 27 he succeeded (1884)
Lord Rayleigh as professor of physics at Trinity College,
Cambridge, and was named director of its Cavendish Laboratory in
the same year, continuing in that position until 1919. Thomson
demonstrated (1897) that cathode rays were actually units of
electrical current made up of negatively charged particles of
subatomic size. He believed them to be an integral part of all
matter and theorized a model of atomic structure in which a
quantity of negatively charged electrons was embedded in a sphere
of positive electricity, the two charges neutralizing each other.
For these investigations he won (1906) the Nobel Prize for
physics; in 1908 he was knighted.
Subsequently, Thomson turned his attention to positively charged
ions. His research showed that neon gas was made up of a
combination of two different types of ions, each with a different
charge, or mass, or both. He did this by using magnetic and
electric fields to deflect the stream of positive ions of neon
gas onto two different parts of a photographic plate. This
demonstration clearly pointed to the possibility that ordinary
elements might exist as isotopes (varieties of atoms of the same
element, which have the same atomic number but differ in mass).
Thomson was a highly gifted teacher--seven of his research
assistants as well as his son, George, won Nobel Prizes for
physics--and he led Great Britain to dominance in the field of
subatomic particles in the early decades of the 20th century. He
was accorded the honor of burial in Westminster Abbey.