Early investigators proposed that the ray of the cathode tube was actually a negatively charged particle because the ray was1 pointattracted to positively charged electric platesdiverted by a magnetic fieldobserved in the presence or absence of a gasable to change colors depending on which gas was within the tube

Early investigators proposed that the ray of the cathode tube was actually a negatively charged particle due to several observations:

1. The ray was attracted to positively charged electric plates: This suggested that the ray was negatively charged, as opposite charges attract each other according to Coulomb's law.

2. The ray was diverted by a magnetic field: This is a characteristic behavior of charged particles. The force exerted on a charged particle in a magnetic field causes it to move in a circular path, which would appear as a diversion of the ray.

3. The ray was observed in the presence or absence of a gas: This suggested that the ray was not dependent on the presence of a gas, and was therefore likely to be a separate entity - a particle.

4. The ray was able to change colors depending on which gas was within the tube: This suggested that the ray was interacting with the gas in the tube, which would be expected if the ray was a stream of charged particles. Different gases would respond differently to being bombarded with these particles, leading to the emission of light of different colors.