I am beginning to learn chemistry/physics, and I have recently read about JJ Thompson's experiment which led to the discovery of the electron. In every source that I've read, the writers note that Thompson used an anode and a cathode to conduct electricity. In addition, the magnet supposedly had N/S ends. I did not know what a charge was, so I looked it up. But, frustratingly, I always get answers that refer to electrons and protons. That is, things that are negative have more electrons than protons, and vice versa. This gives me no idea as to how Thompson inferred that electrons are negatively charged from his experiment.
My question is, can you define charge without talking about electrons and protons? Thompson didn't know electrons existed, so it seems to me that he must've had some other working definition of charge in order to determine that electrons were negatively charged. What makes an object a cathode or an anode, without referring to protons and electrons? If that question doesn't make sense, is it possible to adapt it just for the sake of understanding the experiment?