Theory of the Russell-Hertzsprung diagram.

It is shown how the four first-order differential equations governing stellar equilibrium may be solved directly. Using the solution, the results of current nuclear physics provide a simple and direct explanation of two features of stellar populations known observationally, viz., the mass- luminosity relation and the spectral-type luminosity relation for the main sequence. The observed features of the high-temperature main- sequence stars are given a direct explanation in terms of these results. Relevant properties of the energy-producing mechanism of the giant sequence of stars are deduced from their observed features, and the results compared with those derived on the basis of present-day nuclear theories. The bearing on theories of stellar evolution is explained. Dominion Astrophysical Observatory, Victoria, B. C.