His hard work
He recorded more than 200,000 atmospheric observations in his notebooks, and because of these observations it led John Dalton to study gases, and from the results of his experiments he was able to formulate his atomic theory.
He wondered how water and air could occupy the same space at the same time, when obviously solid bodies can't. He worked a series of experiments on mixtures of gases to determine what effect properties of the individual gases had on the properties of the mixture as a whole.
He modle shows that certain gases only could be combined in certain proportions even if two different compounds shared the same common element or group of elements. Through reseach and experimentation hypothesize that elements combine at the atomic level in fixed ratios. This ratio would be different in the compounds because of the atomic weights of the elements being put together. and thats what his modle shows im the picture above.