J J Thomson's cathode ray tube with magnet coils, 1897.

This apparatus was used to discover the electron. In 1896, in Cambridge, Joseph John Thomson (1856-1940) began experiments on cathode rays. In Britain, physicists argued 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. Apparatus shown without its stand.