John's theory was all matter is made of atoms. All atoms of a given elements are identical in mass and properties. Compounds are formed by a combination of two or more different kinds of atoms. A chemical reaction is a rearrangement of atoms
J.J discovered the electron by or experimenting with a Crookes,or cathode ray,tube. He demonstrated that cathode rays were negatively charged, in addition,he also studied positively charged particles in neon gas.