Sir Joseph John Thomson, English physicist, c 1900s.
© Science Museum / Science & Society Picture Library
In 1896, Sir Joseph J Thomson (1856-1940) began to experiment with cathode rays. In Britain, physicists argued that these rays were particles, but German physicists maintained they were a type of electromagnetic radiation. Thomson showed that cathode rays were particles with a negative charge and much smaller than an atom. These particles were later renamed electrons. In 1912 he went on to develop mas spectrometry. In 1906, he was awarded the Nobel Prize for Physics, for research on conduction through gases.