THE volume on the “Physik des Kosmos,” which forms one number of Muller-Pouillet's “Lehrbuch des Physik,” gives an interesting up-to-date account of astrophysics, looked at from the physicist's point of view. It is edited by Dr. Kopff of Berlin-Dahlem, with chapters by different specialists such as Prof. Emden, who writes on “The Sun.” The German style is on the whole easy and readable, the descriptions of instruments and methods clear, and the work of a high standard of accuracy. As is perhaps inevitable in a work composed by a number of different authors, there is occasional overlapping and a lack of balance between the different branches of the subject. The work of the English mathematicians is very fully discussed, especially the theories of Prof. Eddington. References are freely given in some chapters, but more might have been given with advantage in other chapters, for example, Chap, iii., especially in the summary of theories of stellar radiation at the end. Many familiar photographs are to be found illustrating the chapters on clusters and nebulas, two chapters which seem rather long for the scale of the book. On the whole, the book deals rather more with stellar statistics than would seem to be necessary if written primarily for the physicist. Muller-Pouillets Lehrbuch der Physik. Elfte Auflage. Herausgegeben von A. Eucken, O. Lummer, E. Waetzmann. In funf Banden. Band 5: Physik der Erde und des Kosmos (einschl. Relativitatstheorie). Zweite Halfte: Physik des Kosmos (einschl. Relativitatsiheorie). Herausgegeben von August Kopff. Pp. xii + 596 + 14 Tafeln. (Braunschweig: Friedr. Vieweg und Sohn A.-G., 1928.) 36 gold marks.