Actually, Dalton's Law of Multiple Proportions, which states: "When two elements form a series of compounds, the ratios of the masses of the second element combine with a fixed mass of the first element can always be expressed as the ratio of small whole numbers"; provided Dalton with convincing proof of the existence of atoms. We will not go into this Law. Suffice it to say that it provided necessary background for the existence of atoms. This led to Dalton's "atomic view" of the Law of Definite Proportions. This, in turn, ultimately led to the idea of the chemical formula, such as H_2O, which we take for granted in our modern view of chemistry.