u/BuffaloSpecial8596

I search for it but i always find whatever theory from the atom model. But i want to know first what is it IRL.

Is it something like emitting a light, making it to pass through a gas, and then making it to pass through a prism. So the wavelenghts that dont appear are those absorved by the gas?

I know by that time protons were discovered (in 1886). Maybe it wasnt though they were part of the nucleus, though they were the same charge?

You can say there exists negative particles. But, how do you prove they have mass? How do you know they're in atoms like in the Plum pudding model?