Dalton's atomic theory was first published in:

1. Dalton set out a set of hypotheses about the microscopic features of matter. 2. First published in 1807, many of those hypotheses are still valid in modern atomic theory. 3. They replaced the older idea that matter could be divided without limit. 4. The nineteenth century opening date is what places atomic theory before the discovery of the electron. _Source: OpenStax Chemistry 2e (CC BY 4.0), Ch 2 'Atoms, Molecules, and Ions', sections 2.1-2.6_