Page:Popular Science Monthly Volume 56.djvu/138

130 and apparatus used in studying the physical characters of crystals, and to record and explain the observed phenomena without complex mathematical discussions. The first part of the book relates to the geometrical characteristics of crystals, or the relations and determination of their forms, including the spherical projection, the thirty-two classes of forms, the measurement of crystal angles, and crystal projection or drawing. The optical characters and their determination are the subject of the second part. In the third part the thermal, magnetic, and electrical characters and the characters dependent upon electricity (elastic and permanent deformations) are treated of. A suggested outline of a course in physical crystallography is added, which includes preliminary experiments with the systematic examination of the crystals of any substance, and corresponds with the graduate course in physical crystallography given in Columbia University. The book is intended to be useful to organic chemists, geologists, mineralogists, and others interested in the study of crystals. The treatment is necessarily technical.

A book describing the Practical Methods of identifying Minerals in Rock Sections with the Microscope has been prepared by Mr. ''L. McI. Luquer'' to ease the path of the student inexperienced in optical mineralogy by putting before him only those facts which are absolutely necessary for the proper recognition and identification of the minerals in thin sections. The microscopic and optical characters of the minerals are recorded in the order in which they would be observed with a petrographical microscope; when the sections are opaque, attention is called to the fact, and the characters are recorded as seen with incident light. The order of Rosenbusch, which is based on the symmetry of the crystalline form, is followed, with a few exceptions made for convenience. In an introductory chapter a practical elementary knowledge of optics as applied to optical mineralogy is attempted to be given, without going into an elaborate discussion of the subject. The petrographical microscope is described in detail. The application of it to the investigation of mineral characteristics is set forth in general and as to particular minerals. The preparation of sections and practical operations are described, and an optical scheme is appended, with the minerals grouped according to their common optical characters.

Mr. Herbert C. Whitaker's Elements of Trigonometry is concise and of very convenient size for use. The introduction and the first five of the seven chapters have been prepared for the use of beginners. The other two chapters concern the properties of triangles and spherical triangles; an appendix presents the theory of logarithms; and a second appendix, treating of goniometry, complex quantities, and complex functions, has been added for students intending to take up work in higher departments of mathematics. For assisting a clearer understanding of the several processes, the author has sought to associate closely with every equation a definite meaning with reference to a diagram. Other characteristics of the book are the practical applications to mechanics, surveying, and other everyday problems; its many references to astronomical problems, and the constant use of geometry as a starting point and standard.

A model in suggestions for elementary teaching is offered in California Plants in their Homes, by Alice Merritt Davidson, formerly of the State Normal School, California. The book consists of two parts, a botanical reader for children and a supplement for the use of teachers, both divisions being also published in separate volumes. It is well illustrated, provided with an index and an outline of lessons adapted to different grades. The treatment of each theme is fresh, and the grouping novel, as is indicated by the chapter headings: Some Plants that lead Easy Lives, Plants that know