His work on radiative equilibrium and stellar atmospheres in the 1920s yielded a temperature scale for the sequence of spectral types. With the English mathematician Ralph Howard Fowler (1889–1944) he developed equations which allowed C. H. Payne-Gaposchkin to show that stars are composed largely of hydrogen. In later work on stellar structure he was one of the first to associate nova outbursts with stellar collapse and the emission of a gas shell. In 1932 he turned to relativity and cosmology, showing that there are valid, non-Einsteinian ways of modelling the expanding universe and spacetime.