Dalton’s theory was identified using light microscope images of atoms.
the experimental results of other scientists.
water vapor and air experiments.

Explanation:

Actually it was the experimental results of other scientists. The main stems of the theory was the indivisibility of small spheres (his image) that represented the elements he knew which reacted with other elements.

They seemed to give the same ratios in reactions (definite proportions) and multiple whole number ratios. Look up Lavoisier.