Definition of Thomson, Sir Joseph John
- (1856–1940), English atomic physicist. He discovered the electron, deducing its existence as a particle smaller than the atom from his experiments. Thomson received the 1906 Nobel Prize for Physics for his researches into the electrical conductivity of gases. His son Sir George Paget Thomson (1892–1975) shared the 1937 Nobel Prize for Physics for his discovery of electron diffraction by crystals.