Democitus was a Greek philosophers tha thought of the theory that there were things that were tiny and microscopic called atoms. His experience was if he could keep breaking down the same piece of gold an atom would be the only thing left.
John found that everything is made of atoms and all atoms of a given element are identical in mass and properties. A chemical reaction is a rearrangement of atoms. He found this while doing something with gases.
Crookes studied the effects of sending an electric current through gas in a sealed tube. He noticed that as you removed gas from a tube, a glow would appear if you place a high voltage across it. He called them cathode rays.
Rutherford tested Thomson's hypothesis by devising his "gold foil" experiment. Rutherford reasoned that if Thomson's model was correct then the mass of the atom was spread out throughout the atom. He inferred a small, dense, positively-charged nucleus.