Course in Astrophysics. Vol. III. A. A. Belopolsky, Astrospectroscopy. 277 pp. Petrograd. 1921. Vol. I. G. A. Tikhov. Astrophotometry. 131 pp. “Scientific Book Publishing House,” Petrograd. 1922.

The Scientific Book Publishing House in Petrograd is publishing a course in astrophysics, of which the two above-mentioned volumes have so far appeared. Subsequently three more volumes are to appear, namely: Astrophotography by S. K. Kostinsky, Stellar Statistics by V. V. Serafimov, and an additional volume by O. D. Khvolson. Written by the most prominent Russian specialists, this course undoubtedly represents an outstanding phenomenon in Russian scientific literature. But even in foreign literature one cannot point to a book such as Belopolsky’s Astrospectroscopy. The contents of this third (the first to appear) volume of the course consist of three parts. In the first of

they describe instruments and methods of measurement. Spectroscopes of various kinds, spectrographs, a spectrocomparator, a spectral photometer, and other instruments are described here. Exceptionally valuable features of the exposition are the many small but very important details both in the construction of the instruments and in working with them. These details are precisely what distinguish the master from the dilettante. Further, the numerous examples, taken for the most part from the author’s rich material, are very valuable. In the second part various laws of radiation are set forth, beginning with Kirchhoff’s law and ending with the quantum theory and Bohr’s theory. Here, among other things, the author’s classical investigations on the experimental verification of the Doppler–Fizeau principle are described. In the third part the results of applying spectral analysis to the study of the structure and motion of various celestial bodies are described. A brief bibliographical guide is appended at the end. Alongside the enormous merits of this book, from which one can learn how to work and which acquaints the reader with the spirit of modern investigations, one must nevertheless note a certain lack of restraint in the exposition, where some questions are treated very thoroughly, while others are touched upon only very briefly. One may also regret the absence of a detailed subject index. But in general it may be said of this volume of the course that it was written by the foremost specialist in this field in Russia and is of quite exceptional interest.

Turning to the first volume of the course—Astrophotometry by G. A. Tikhov—we shall first of all note its contents. The book consists of four sections, of which the first is devoted to visual photometry. Here photometers of various systems and the results of work with them are described. In the second section, perhaps the most valuable and interesting one in view of the absence of literature on this subject in Russian, the foundations and methods of photographic photometry are set forth. The third section concerns questions connected with the color index of stars. Finally, in the fourth section the principal questions of spectrophotometry are concisely presented, including the method of light filters. Thus in its content the book is of great interest. We know of no other course or monograph, even in foreign literature, in which all methods of photographic photometry are described. But, despite its great merits, the book also has its shortcomings. Among these must be counted excessive brevity, at times a schematic character of the exposition. The book lacks technical indications as to how a given measurement is made, how the instrument is handled, and so on. If it is true that one can learn the practice of astronomical observations only under the guidance of a specialist, then perhaps such indications are unnecessary in the book. Nevertheless, the reader who has read Astrophotometry, although he will learn about the construction of modern instruments and about the methods of investigation, will not learn how to pro—

the investigation itself is carried out, he will not learn. It should also be pointed out that the book does not touch at all upon two very important methods of modern photometry: the use of the selenium photometer and of the photoelectric effect. If the first of these has played only a transient role in photometry and, because of the difficulty and complexity of the apparatus, has almost been abandoned, the second has already yielded remarkable results and undoubtedly has a great future. Further, the book leaves aside important questions, partly of an instrumental and partly of a theoretical nature. Such are the questions of atmospheric extinction, of the influence of phase, and, in general, the laws of reflection and scattering of light. In connection with the latter it should also be noted that Tikhov’s Astrophotometry is, in essence, confined only to the photometry of stars, whereas photometry, as a part of astrophysics, includes the study of the sun, the moon, planets, comets, nebulae, and star clusters.

Nevertheless, it must be acknowledged that the publication of the first volume of the course in astrophysics is of hardly less significance for Russian science than the earlier publication of the third volume, especially if one takes into account that photometric work, being considerably simpler on the instrumental side, is far more accessible to broad circles of astronomers, both specialists and amateurs, than spectroscopic investigations. One can only welcome the parts of the course in astrophysics that have appeared and wish for the speedy publication of the remaining parts.

A. Mikhailov.