John Dalton was a renowned English chemist, physicist and meteorologist. John Dalton contributed a lot to science, but the most important contribution he made was those of understanding atoms. His contribution was the Atomic Theory. This theory suggests that all matter is composed of indivisible and indestructible atoms with distinct masses and properties. 

Dalton did many experiments to prove his theory. One example of his experiments is when Dalton combined oxygen with one or two volumes of nitric oxide in closed vessels over water. 

This is the Billiard Ball Model. This is what Dalton envisioned of an atom. Dalton imagined them being extremely small, solid, and hard like a billiard ball. 

One interesting fact about John Dalton is that he was colorblind. Dalton often confused the color scarlet with pink, green and blue.