Sir Joseph John "J. J." Thomson, OM, FRS (18 December 1856 – 30 August 1940) was a British physicist. In 1897, Thomson showed that cathode rays were composed of a previously unknown negatively charged particle, and thus is credited with the discovery and identification of the electron. Thomson is also credited with finding the first evidence for isotopes of a stable (non-radioactive) element in 1913 as part of his exploration into the composition of canal rays (positive ions) and with the invention of the mass spectrometer. Thomson was awarded the 1906 Nobel Prize in Physics for the discovery of the electron and for his work on the conduction of electricity in gases.