Joseph John Thomson was born in 1856 at Cheetham Hill - near Manchester. He studied sciences in Manchester. After studies he moved to Cambridge, were he became Rayleigh's assistant. After Rayleigh had left, at the age of 28 Thomson became the head of the experimental physics faculty and of the Cavendish Laboratory. He was also a lecturer at the universities in Princeton and New Haven (the Yale University) in the United States.
His major achievement was the determination of the ratio of charge to mass of the molecules composing cathode radiation, and the conclusion that those rays consisted of identical molecules, which were called electrons (he presented this hypothesis on 30th April 1897). Thomson perceived an atom as a charged sphere with electrons inside (the "plum cake" model). That model was good enough to explain many physical and chemical phenomena - electrolysis, electron emission.
The scientist also discovered that in the substances he researched the number of electrons in an atom equalled half of the mass number. He investigated and analysed beams of positive ions emerging at the cathode inside the tube, similar to the one due to which he discovered electrons. In 1913 together with Francis Aston he discovered the existence of permanent neon isotopes.
In 1906 Joseph John Thomson received a Nobel prize.
In 1915 he became the chairman of the Royal Society. He remained in the position until 1920 when he withdrew from scientific activity. Thomson died on 30th August 1940.