Page:Popular Science Monthly Volume 51.djvu/577

Rh by the use of simple language and many photo-engravings of well-selected specimens he makes their nature remarkably clear. In the dynamical division the processes of weathering, erosion, deposition, stratification, metamorphism, and the formation of mountains, volcanoes, etc., are made clear by the same means. The stratigraphical division probably contains as much material as the pupil is likely to assimilate. It opens with an explanatory chapter on the uses of fossils, then the kind of life that prevailed in each geologic age is described with the aid of figures of fossils and ideal landscapes of the several ages, and the account closes with an outline of the changing geography of the United States from Archæan to Cenozoic time. Throughout the work the author is careful to distinguish important doctrines that are proved from those that remain hypothetical. The volume is printed in large, clear type, and contains two hundred and sixty-eight figures and twenty-five plates, including a colored geological map of the United States.

His various investigations and writings, extending over a term of years, have well equipped Prof. Israel C. Russell with material for making a book on the North American glaciers. In the volume which he has recently put forth he not only enumerates and describes the glaciers of this continent that have been explored, but he also explains the theory and depicts the behavior of these solid rivers, so that the reader untrained in science may follow him. The glaciers of the Alps, being in a region that is surrounded on all sides by thickly populated countries, have been the most studied. But Prof. Russell points out that "North America offers more favorable conditions for the study of existing glaciers and of the records of ancient ice sheets than any other continent. Of each of the three leading types of glaciers thus far recognized—namely, the Alpine, Piedmont, and continental—North America furnishes magnificent examples." After describing the glaciers of each locality from the Sierra Nevada Mountains to Greenland, our author discusses the climatic changes indicated by the glaciers of North America and the evidence that the great ice sheets are retreating. The how and why of glacier movement, and the life history of a glacier, form the subjects of the two closing chapters. The volume is illustrated with twenty-two plates and ten smaller figures.

"There is perhaps little that need be said prefatory to a work of this character," say the authors of a volume of problems, and for the same reason a description of the work can not be long. The authors have prepared it in the belief that any text in physics needs to be supplemented by problem work in considerable variety. An introduction contains the tables of physical constants required in working the problems, while tables of logarithms, sines, etc., and a fist of answers appear at the end of the volume. The use of directed quantities, graphic methods, averages, and approximations is briefly set forth in several preliminary chapters. The problems are divided among the subjects of mechanics, solids, the behavior of liquids and gases, beat, electricity, magnetism, sound, and light. A few problems have been inserted which can not be satisfactorily worked by other than calculus methods, while here and there graphic methods have been suggested that may be profitably extended by the student. Occasional questions not requiring numerical answers have been asked.

The fourth volume of the American History Series deals with a period of growth. Between 1817 and 1858 the territory of the United States was increased by the acquisition of Florida, Texas, and Oregon. The population of the older States, pushing toward the west and southwest, made settlements and organized communities in the hitherto unorganized territories. In this task they were largely re-enforced by immigrants from Europe. It was a period also of the growth of pent-up forces, which later produced the outbreak of the civil war.