NEW BOOKS Report on Band-Spectra of Diatomic Molecules. By W. JEVONS, D.Sc. 26 x 18 cm.; viii 308 pp. London: The Physical Society, 1932. Price: (paper covers) 17s. 6d. net; (in cloth) 20s. 6d. It is difficult t o rate this book too highly. The author has devoted some three years t o its preparation, and remarkable clarity of exposition and care for detail are maintained throughout, betraying no signs of any desire to hasten a conclusion. This is praiseworthy in view of the rapid development of the mechanical significance of band-spectra, and it is indicative that such a lengthy report can be written from the “observational, rather than the purely theoretical, aspect of the subject.” We may take this as signifying t h a t the fundamental principles are so firmly established that the “theoretical results necessary for the interpretation of the analyses of bands and band-systems” may be “briefly stated, with no indication of the quantummechanical methods used in their derivation.” This is now possible, whilst only a few years ago textbooks on spectroscopy essentially dismissed the whole of bandspectra with a casual reference to their probable association with molecules. The report, in the words of the author, is “mainly addressed to the physicist who has not hitherto taken up band-spectra as a subject for special reading or laboratory work;” in the opinion of the reviewer the author should have made wider claims, since the larger proportion of chemists are unfamiliar with the modern interpretations of the fundamental principles of their science by mathematical physicists. Here is an opportunity for the chemist to see how the spatial and thermal properties of molecules are rigorously defined by spectroscopy, how conceptions of valency are being altered and extended, and how the excitation of individual molecules as a necessary preliminary to chemical reaction is bound up with alterations in their detailed electronic structure, the conditions and consequences of such alterations being well on the way to spectroscopic determination. I n short, we may be nearing the time predicted by Mulliken when the achance of mathematical technique is such that it may be easier to calculate the properties of polyatomic molecules than to determine them experimentally. It is to be emphasized that however clear, logical, and fluent the presentation of the results and conclusions in spectroscopic work may be-and the present report is a model in that respect-no benefit is likely to be derived from casual reading. This is due partly to the complexity and all-embracing nature of the subject, and partly to the extensive notation required, and the author does well to insist upon frequent reference t o the valuable glossary offered in Appendix I. Mulliken’s notation as used, although i t has produced order out of chaos, has rendered more complicated some of the simpler expressions familiar to spectroscopists, and may need further revision when our knowledge of the band-spectra of polyatomic molecules approaches a similar finality. Certain matter, generally of a descriptive nature, has been relegated to small type, with the suggestion that it might be omitted by the “more casual reader,” but if this process is applied to Chapter V, dealing in a most able and concise way with line-spectra and the electronic states of atoms, this reader will find the remaining half of the book largely unintelligible. Nothing but praise is to be found for the
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typography of the Cambridge Press, and for the sixty-four diagrams, all of which seem to have been specially prepared by the author for the report. It is hardly possible to select any portion of the book for individual praise, but the chapter on the isotope effect is well done, and represents the first reasonably complete account of the phenomenon. As an indication of how far the references are up-todate, one may cite the identification of H2 (page 211), and the isotopes of germanium (page 227). The most valuable feature from the point of view of those already working in the field of band-spectra lies in the table of constants for electronic states and band-systems given in Appendix 11. The foreword to the Appendix should be consulted for an appreciation of the possibilities offered by the data provided, and although any approach to completeness is disclaimed, it is difficult to see what purpose would be served by any further search of the literature b y those interested. The time is scarcely ripe for a similar report dealing with the theoretical significance of the observed results, and the author has probably done wisely in attempting no discussion of such problems as valency. The stress on the observational aspect leads to the dismissal of the phenomenon of predissociation in two pages, and one can but wait with great interest for the eventual appearance of a companion volume. The work as i t stands is a magnificent achievement, and the highest praise is due to the successful collaboration of the author, printers, and publishers. C. R. BAILEY.
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The Method of Dim,ensions. By PROF.A. W. PORTER, F.R.S. 17 x 11 cm.; v 80 pp. London: Methuen and Company, 1933. Price: 2/6. I n this volume, one of the recent additions to Methuen’s series of short monographs on physical subjects, Professor Porter has collected together important applications of the method of dimensions. The more fundamental and still controversial subject of units has up t o the present time had the greater attention, and the author has done well to bring t o our notice the existence of a very useful tool. It is important however that the student should realize the limitations of the method; it should be used only when other methods of approach have failed to give an understanding of the physics of the problem. A little greater emphasis on this aspect of the subject, together with a rather more extended introductory treatment of units, would perhaps have increased the value of the book, particularly for the physical chemist. A historical introduction stressing the fundamental work of Newton, and, later, of Fourier, leads the way to discussion of such problems as the time of swing of a simple pendulum, the flow of fluids, surface tension, and heat effects. A final section deals with electromagnetic and electrostatic units. Many references t o original papers and summary articles are given and one or two blank pages a t the end are available for notes. The present writer had hoped to aee, from the point of view of historical interest, some reference to Einstein’s early application of the method of dimensions to the determination of the frequency of vibration of atoms in a solid body. This is not, however, to detract from the large amount of useful information which Professor Porter has set before us, and the book will be of considerable value to all students of physics and physical chemistry. J. T. RANDALL. Gmelins Handbuch der anorganischen Chemie. 8 Auflage. Herausgegeben von der Deutschen Chemischen Gesellschaft. System-Nummer 30: Barium. 26 x 18 cm.; xviii xvi 390 pp. Berlin: Verlag Chemie G. m. b. H., 1932. Price: 64 M. (subscription price 56 M.). This volume gives a very complete account of the chemistry of barium and its compounds and is complete in itself. There are thirty-one figures in the text. The
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