Thomson's main focus on his studies & his theory?

In 1894, Thomson began studying cathode rays, which are glowing beams of light that follow an electrical discharge in a high-vacuum tube.

In 1897 the British physicist Joseph John Thomson, discovered the electron in a series of experiments designed to study the nature of electric discharge in a high-vacuum cathode-ray tube.

In 1904 Thomson suggested a model of the atom as a sphere of positive matter in which electrons are positioned by electrostatic forces.

"Plum Pudding Model"