REVIEWS 359 



of using the same means, an induction coil, for producing the electrons from the 

 metal cathode as for accelerating them sufficiently through the vacuum to 

 generate X-rays by impact upon the target, the operation may with advantage be 

 done in stages, and more appropriate means devised for the two stages separately 

 than for both together. Thus the Coolidge X-ray tube, described fully in one of the 

 appendices, which so far has hardly been tried in this country, generates its electrons 

 from an incandescent coil of tungsten wire, and operates therefore in an absolute 

 vacuum. Whether it justifies itself or not in practice, it is clear that some 

 knowledge of the theory of electrons and X-rays, beyond that which sufficed for 

 the earlier pioneers, is likely to prove very useful and interesting to the large and 

 increasing number of people who use X-rays in their daily work. 



Judged by the following sentence in the introduction, which it is only fair to say 

 is not representative of the quality of the book, the author appears to take a some- 

 what narrow and partial view of the recent profound changes which have over- 

 taken physical science, for it would be difficult to give an adequate historical 

 justification for the statements it contains. We read : "The discovery of electrons 

 provided us with the present accepted theory of the constitution of matter ; it paved 

 the way for a ready recognition of the properties of the radioactive elements, then 

 on the point of discovery ; and it led to a new school of physics which accepted as 

 a creed the transmutation of the elements, an idea utterly repugnant to the 

 orthodox chemist who had been taught to regard the elements as fundamental 

 and immutable. . . ." Whether any one is so foolish as to accept 

 transmutation as a creed now or not, it is some eleven years since it was 

 established as a fact in the domain of the radio-elements by the researches of 

 chemists equally with those of physicists. The suggestion that the electron or 

 the electrical theory of the constitution of matter played any part at all in 

 the establishment of the fact is unfounded. If that theory is really accepted at 

 the present time it must be rather as a creed than as established by experiment, 

 for it fails to account for more than one two-thousandth part of the mass of matter. 

 Though as a first step it has proved itself extremely suggestive and fruitful in 

 almost every direction, and doubtless in time will assist in the still unsolved 

 problem of artificial transmutation. 



The time is just ripe for the appearance of a good book on the X-rays. The 

 work of Laue and his colleagues on the reflection of X-rays from crystal surfaces, 

 has shed light on many problems, and most of all on the nature of the X-rays 

 themselves, the name of which is now a misnomer after eighteen years of appropriate- 

 ness. These researches and the corresponding ones of the Braggs, Moseley, and 

 others in this country, although so recent, occupy an important place in the present 

 volume. In an appendix, Sir James Mackenzie Davidson, one of the earliest 

 pioneers in the medical uses of the X-rays in this country and the inventor of 

 stereoscopic methods of localisation, contributes an interesting interview with 

 Prof. Rdntgen at Wurzburg soon after the famous discovery. 



F. S. 



An Introduction to the Study of Organic Chemistry. By H. T. Clarke, 

 D.Sc, F.I.C. [Pp. viii + 484, with diagrams.] (London : Longmans, 

 Green & Co., 1914. Price 6s. 6d.) 



In compiling this book the author's intention has been to display the orderly 

 principles and structural unity'of organic chemistry rather than to direct attention 

 to details, and descriptions of practical methods are accordingly omitted. 



