How did we figure out atoms exist?

In 1808, chemist John Dalton developed a very persuasive argument that led to an amazing realization: Perhaps all matter (i.e., stuff, things, objects) is made of tiny, little bits. Fundamental bits. Indivisible bits. Atomic bits. Atoms.

The concept had been floating around off and on for a few millennia. Ancient cultures were certainly aware of of the general idea that matter was composed of more fundamental elements (though they disagreed quite a lot about what exactly counted as an element) and knew that these elements combined in interesting and fruitful ways to make complex things, like chairs and beer. But through those millennia, the question persisted: If I isolated a single element and chopped it in half, then chopped those halves in half, and so on and so on, would I eventually find a smallest possible bit of element that I could no longer chop? Or would it go on for infinity?

https://www.space.com/how-did-we-discover-atoms.html