This work develops and defends an early atomic theory of matter, presenting experimental observations and tables of relative atomic weights and showing how chemical substances combine in simple, fixed ratios of indivisible atoms. It applies the theory to gases, oxides, salts and other compounds, explains stoichiometric relationships (including the law of multiple proportions), gives worked examples and calculations, and uses empirical evidence to argue that atomic ideas provide a coherent, predictive framework for understanding chemical reactions and compound formation.