The main part of Dalton's atomic theory that was later proven incorrect is the idea that atoms are indivisible.

Here's a breakdown:

* Dalton's theory: Atoms were the smallest unit of matter and couldn't be broken down further.

* Later discoveries: The discovery of subatomic particles like electrons, protons, and neutrons, proved that atoms are actually made up of smaller components.

While Dalton's theory laid the groundwork for our understanding of atoms, it was eventually refined by later scientists.