How was Atomism discovered?

Question

How did Democritus and Leucippus find the fact of Atomism?

Answer 1

It was strict a thought experiment.

Aristotle thought that if you take any object you can continue to break it in half forever without ever coming to an end. (kind os like if you continue to go each tiome half way towards a wall you will never reach the wall.
Democritus reasoned that eventually you would have to get a piece that could no longer be cut in half. He called this piece atomos which is greek for indivisible.
Neither person could test their theories so it stayed that way for almost 1800 years.