marks that the "discrepancy" in Eddington's theory regarding the opacity of stellar interiors can be removed by assuming that the star is almost entirely of hydrogen. I have been for some time past engaged in an accurate evaluation of the opacitycoefficient (which is defined as the Rosseland mean) and the absorption-coefficient (which is defined as the Straight mean). Since Professor Menzel does not explicitly mention what formula he uses, and since as far as I am aware the accurate formulae are nowhere given, the following results of mine may be of interest. The atomic absorption-coefficient of pure hydrogen is given by the formula