sir joseph john "j.j." thomson, om, frs (18 december 1856 – 30 august 1940) was a british physicist and nobel laureate. he discovered the electron and isotopes, and invented the mass spectrometer. he was awarded the nobel prize in physics in 1906 for his discovery of the electron and his work on the conduction of electricity in gases. john joseph thomson in 1893 said: "there is no other branch of physics which affords us so promising an opportunity of penetrating the secret of electricity."