Thompson was born in the suburbs of Manchester December 18, 1856. He attended Owens college in 1870, Trinity college in 1876 and was master of Trinity college by 1918
Thompson carried out his research on cathode rays in the Cavendish laboratories where he was the professer of experimental psysics.
J.J. Thomas discovered the electron whilst investigating cathode rays. Cathode rays are ray like eminations proceded from a cathode electrode to an anode electrode which occur when electricity is passed through air evacuated tubes containing electrodes.
Thompson discovered that these that these rays held a negative charge when he put a negativly charged plate on one side of the rays and a positive on the other. He observed that the rays were deflected towards the positive plate and therefore concluded that the rays held a negative charge.
A second test was used to deduce that these rays had a mass.
A shaddow was cast in the path of the rays, the only way that these rays could cast a shaddow on the back of the tube would be if they had momentum, and if they possesed momentum then it must mean that they also posessed mass, because,
Momentum = Velocity x Mass... so now it was experimentally determined that these cathode rays posessed both a finite mass and negative charge. He named thse particles 'corpuscles' and proposed that they exist inside atoms, which was a bold statement at the time as it was believed that atoms were the most fundamental unit of matter.
As it turns out, Thompson was correct and we now know these particles to be electrons.