Here's how he did it:

* Cathode Ray Tubes: Thomson studied the behavior of cathode rays, which are beams of electrons emitted from the cathode of a vacuum tube.

* Electric and Magnetic Fields: He observed that cathode rays could be deflected by both electric and magnetic fields. This indicated that the rays were made up of charged particles.

* Charge-to-Mass Ratio: He meticulously measured the deflection of the rays in known electric and magnetic fields, allowing him to calculate the ratio of the charge of the particles to their mass (e/m).

* Universality: Thomson found that the e/m ratio was the same regardless of the material used to make the cathode, suggesting that the particles were fundamental building blocks of all matter.

While Thomson didn't directly "see" electrons, his experiments provided compelling evidence for their existence and led to the determination of their fundamental properties.

It's important to note that the term "electron" wasn't coined by Thomson. It was first suggested by George Johnstone Stoney in 1891, who was studying the nature of electricity.