Bibliography

O. Dorno. Physik der Sonnen- und Himmelstrahlung (Die Wissenschaft. Einzeldarstellungen aus der Naturwissenschaft und der Technik, herausgegeben von Prof. Dr. Eilhard Wiedemann. Bd. 63). Fr. Vieweg und Sohn, Braunschweig, 1919. pp. VIII + 126.

The series of books “Die Wissenschaft” has as its aim to acquaint a broad circle of readers with contemporary views on scientific and natural-historical questions. The 63rd issue of this series is devoted to the physics

the radiation of the sun and of the celestial vault. From the title alone it is already clear that the subject under discussion falls into two closely connected questions: between the source of radiation—the sun—and its receiver—the earth—there lies a transmitting medium, the atmosphere, which is itself subject to the action of the sun and for the earth becomes a secondary source of radiation, while at the same time altering the energy penetrating it. The study of solar activity is thus reduced to the study of secondary phenomena, by which one must judge the primary source. All discussions are conducted, as is customary, on the assumption that the sun and the atmosphere are unchanging. Only at the end of the book does the author devote several pages to the question of changes in solar activity. If the atmosphere remained constant, it would not be difficult to trace the changes in the primary source. But the activity of the sun first of all affects the structure of the atmosphere itself, and different parts of solar energy produce different effects. The picture is further complicated by the fact that a change in solar activity causes volcanic activity in the earth, which, owing to eruptions, also influences the activity of the atmosphere. Naturally, the author, deeply devoted to his subject and having spent many years studying solar activity in Davos, calls for systematic observation of radiations.

The book brings together all the rich experimental material of recent years, clearly analyzed and systematized. At the beginning a clear picture is given of the structure and composition of the atmosphere. Then the question of the radiation of the sky is examined. Of particular interest is the chapter on the spectral investigation of solar radiation. A great deal of work in this direction has recently been done by the Americans, who have at their disposal the large resources of their patrons. The most important observations were carried out on Mount Wilson in California at an altitude of 1730 meters, then in Washington almost at sea level and, finally, on Mount Whitney in California at an altitude of 4420 meters. In addition, two expeditions were equipped to Algeria, to Bassour, at an altitude of 1160 meters, at a distance of one third of the earth’s circumference from the observatory on Mount Wilson. All the observations provide material comparable with one another: the observations were made, as far as possible, simultaneously and with identical instruments. From the physical point of view, Langley’s spectrobolometer and its successor, Abbot’s, are of interest; the author describes it in detail and gives samples of the curves obtained. The photographing of the whole spectrum takes place over 11 minutes, a time during which the height of the sun and the state of the atmosphere may be regarded as unchanged. The photographs are made at different solar altitudes. From the spectrograms obtained one can study the distribution of the sun’s energy both at the boundary of the atmosphere and at the earth’s surface.

The second half of the book is devoted to the question of the radiation of the celestial vault. Since, by the very nature of the book, the author avoids mathematical analysis, here too he does not make use of it,

but clearly sets forth the essence of those physical phenomena that constitute the radiation of the vault of heaven. The chapter on the polarization of the sky, with its concise and complete picture of the observed phenomena, is interesting. All the questions are accompanied by abundant information on the results obtained from observations, from which the author immediately indicates the possibility of conclusions for synoptics (polarization) or for therapeutic purposes (the tasks of health resorts). It should be mentioned that in the text everywhere the author refers to the literature of the question and gives very precise information about instruments. Unfortunately, the language of the book is very difficult, so that even with a good knowledge of the language it is not easy to read, although all difficulties are compensated by the interest of the content and the depth with which the subject is treated.

A. Fernik.