Studies on multiple scattering and radiative transfer began early in this century by the work of Schwarzschild, Miln e, and Eddington. In the 1950's the important books of Chandrasekhar, Kourganoff and Sobolev on this subject appeared.
In spite of the fact that almost all important questions in this very classical problem have now been solved, it often takes long to obtain the numerical answer to a simple question. For that reason I stated some years ago to prepare a book which should contain many tables and graphs together with a condensed text. In the course of this work it was found useful to deviate from normal usage in some respects, which I shall briefly review.