Dalton didn't conduct a single, groundbreaking experiment that directly led to his atomic theory. His theory was built upon the work of many scientists before him and his own meticulous observations and calculations. Here's how he came to his conclusions:

* Observations of Chemical Reactions: Dalton observed that chemical reactions always involved the same ratios of reactants and products. This observation, known as the Law of Definite Proportions, suggested that elements combine in fixed proportions, implying the existence of fundamental units – atoms.

* Law of Multiple Proportions: Dalton further observed that when two elements combine to form more than one compound, the masses of one element that combine with a fixed mass of the other element are in simple whole-number ratios. This law reinforced his idea of indivisible atoms combining in specific ratios.

* Analysis of Gases: Dalton also studied gases and their behavior, especially the pressure exerted by different gases. His observations led him to propose that atoms are in constant motion and exert pressure through their collisions.

* Calculations and Deductions: Dalton meticulously collected data and used it to calculate the relative atomic weights of different elements. His calculations were based on the assumption that atoms of different elements had different weights.

In summary, Dalton's atomic theory was not based on one specific experiment but rather on a combination of:

* Observations of chemical reactions and their ratios

* Analysis of gas behavior

* Mathematical calculations and deductions

It's important to note that Dalton's theory was not without flaws and later scientists refined and expanded upon it. Nevertheless, it laid the foundation for our modern understanding of atoms and the structure of matter.