No one needs to be reminded of the importance of this subject to industry, and the progress made in recent 5:ears. Present knowledge of metals has come, very largely, from the application of scientific methods to their investigation. The many different methods in use have resulted in two conditions, (I) that there is a lack of familiarity with the limitations, purposes, and accuracy of some of the methods by those who may profit thereby, and (2) that there exists a feeling among many, who apply the methods, that certain of them are better than others, which condition is due to greater knowledge of some than others. Undoubtedly, a clarification of this matter will further metallurgical technique.
The two volumes, at hand, comprise a set. Volume one treats on optical methods of examination of metals. It gives a brief introduction on the main properties of light, and proceeds through geometrical optics, wave optics (which is divided into parts on interference and on diffraction), polarised light, and a final chapter on sources of light.
Volume two is devoted to electrical methods. Under the heading of magnetism, methods are described for testing irregularities, detecting flaws, and other purposes.
Electrical measurements are treated, on including the use of thermoelectric effects to study metals, and electrical methods of measurement of thickness from one side. A very interesting and well-arranged chapter is that devoted to x-ray diffraction. There is described the Finch electron diffraction camera, and considerable attention is given to the electron microscope and the subject of radiography. Details of the process of electrolytic polishing, as applied to a numberof metals, are given in Appendix I, while Appendix II consists of various x-ray data that are useful for reference.
The books give adequate explanation of the theory underlying the physical examination of metals together with a description of the more important a]3plications that have been made, and to a limited extent, a description of the technique. They are valuable to all those having to do with the examination of metals, and their use should encourage the employment of suitable and best methods. R. H. OPPERMANN.