Apparatus used by JJ Thomson to discover the electron, 1897.
© Science Museum / Science & Society Picture Library
An illustration of the apparatus used by Thomson to discover the electron, taken from his paper in 'Phil Mag' (1897). In 1896, in Cambridge, (Sir) Joseph John Thomson (1856-1940) began experiments on cathode rays. In Britain, physicists argued that these rays were particles, but German physicists disagreed, thinking they were a type of electromagnetic radiation. Thomson showed that the cathode rays were particles with a negative charge and much smaller than an atom. He published this information in April 1897; the particles were later named electrons.