He is better remembered, however, for his researches into physical chemistry. In 1815, based on the tables of atomic weights available at the time, he hypothesized that the atomic weight of every element is an integer multiple of that of hydrogen, suggesting that the hydrogen atom is the only truly fundamental particle, and that the atoms of the other elements are made of groupings of various numbers of hydrogen atoms. While Prout's hypothesis was not borne out by later more accurate measurements of the atomic weights, it was a sufficiently fundamental insight into the structure of the atom that in 1920, Ernest Rutherford chose the name of the newly-discovered proton to, among other reasons, give credit to Prout.
Prout contributed to the improvement of the barometer, and the Royal Society of London adopted his design as a national standard.