* Thomson conducted experiments using cathode rays, which are streams of electrons emitted from a negatively charged electrode (cathode) in a vacuum tube.

* He observed that when cathode rays passed through a magnetic field, they were deflected.

* The direction of deflection depended on the polarity of the magnetic field and the charge of the particles.

* Positively charged particles would deflect in one direction, while negatively charged particles would deflect in the opposite direction.

Measurement of the charge-to-mass ratio (e/m)

* Thomson also measured the charge-to-mass ratio (e/m) of the particles in cathode rays.

* He did this by using a combination of electric and magnetic fields.

* The electric field was used to accelerate the particles, while the magnetic field was used to deflect them.

* By measuring the amount of deflection and the strength of the electric and magnetic fields, Thomson was able to calculate the e/m ratio.

Discovery of the electron

* Thomson's experiments showed that cathode rays consist of negatively charged particles that have a much smaller mass than atoms.

* He concluded that these particles must be a new type of subatomic particle, which he called "electrons".

* The discovery of the electron was a major breakthrough in physics, and it paved the way for the development of our modern understanding of the atom and the fundamental particles of matter.