What Is the Charge Experiment?

When you heat it up, it spits out electrons and then the electrons interact with the atoms in the gas. It's presumably chosen so that it releases a photon of a specific wavelength through that interaction. So what they again saw were these light rays or these rays again deflected towards the cathode. And from that whole analysis they discovered that this thing, this alloy is releasing things that for some reason is going towards the positively charged plate of this electric setup. What must this be? Hence the discovery of the electron.