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on previous accounts of -a similar character, but special attention should be 

 directed to the discussion on series notations, where a very clear statement 

 is given of the points of difference between Paschen's revised notation and 

 that employed by Fowler in his Report on Series in Line Spectra. The need 

 for a standard system of notation is becoming urgent ; it is therefore par- 

 ticularly unfortunate that these new and authoritative systems should have 

 several serious points of difference. It would seem that the time is almost 

 ripe for an international discussion on this question, when it would probably 

 be found possible to incorporate in one system the best features of both. 



After a brief exposition of " energy diagrams " the subject of ionisation 

 and resonance potentials is dealt with, and here it is somewhat disappoint- 

 ing, especially in view of the authors' wide experience in these matters, to 

 find no account of the experimental methods employed in this difficult but 

 fascinating field. Next follows a very valuable chapter on line absorption 

 spectra, in the course of which there is a discussion of some highly interesting 

 results in connection with the determination of "t," the average time of 

 sojourn of an electron in an outer orbit. Here is probably a line of advance 

 which may lead far. The chapter on thermal excitation and correlation 

 of spectral phenomena with temperature is a very striking one, and contains 

 an adequate summary of Saha's astrophysical work, the details of which are 

 perhaps less familiar to physicists than they should be. The account of 

 X-ray spectra is particularly clear, and will go far towards dispelling the 

 bewilderment which the present nomenclature is apt to inspire in those who 

 have no specialised knowledge of this region of the spectrum. 



Appendix I contains a chart from which may be read off approximate 

 values of such quantities as electron velocities and wave-lengths radiated 

 (for a given accelerating voltage) and so forth. Comparatively few, perhaps, 

 will make use of this, but those who do are likely to find it invaluable. 

 Appendix II consists of a ten-page summary of Bohr's recent lengthy paper 

 [Zeitschrift f. Phys.) setting forth his new theory of atomic structure. 



References to original papers are numerous and are brought right up 

 to date, and there are a number of very excellent plates. 



W. E. C. 



CHEMISTRY 



An Inorganic Chemistry. By H. G. Denham, M.A., D.Sc, Ph.D., Pro- 

 fessor of Chemistry, University of Capetown. [Pp. viii + 684. 

 Illustrated.] (London : Edward Arnold & Co., 1922. Price 12s. 6d. 

 net.) 



It is pleasant in these days of high-priced books to welcome a textbook 

 on chemistry at a moderate price, and although one swallow does not make 

 a summer it may be reasonably regarded as an omen of better times to 

 come. 



Prof. Denham has given special prominence to the Periodic System in 

 his book. After considering the reactions of the halogen and oxygen families 

 of elements, the Periodic System is carefully dealt with and made the basis 

 for the study of the remaining elements. 



The ionic theory is not discussed until the non-metals have been dealt 

 with, and in this way the electrolytic theory of solution forms a useful 

 introduction to the study of the metals and their salts. 



The book is clearly and concisely written, but is not overloaded with 

 details of unimportant substances and other side-issues, and affords a useful 

 introductory textbook on inorganic and general chemistry for students, and 

 especially for those studying other branches of natural science who need 

 a complete and thorough grounding in the fundamentals of chemical science. 



F. A. M. 



