Original: Sir Joseph John '' J. J. '' Thomson , OM , FRS ( 18 December 1856 30 August 1940 ) was a British physicist and Nobel laureate , credited for the discovery of the electron and of isotopes , and the invention of the mass spectrometer .
Simplified: Sir Joseph John '' J.J. '' Thomson , OM , FRS ( 18 December 1856 30 August 1940 ) was a British physicist and Nobel laureate , that discovered the electron and isotopes , and invented the mass spectrometer .