X‐ray optics. The diffraction of X‐rays by finite and imperfect crystals by A. J. C. Wilson

No living branch of science is static. As it develops it may change its form, and such changes must be reflected in the way tha t the subject is presented to the newcomer to the field. Only by seeing the fundamentals presented unclouded by the errors and obscurities of the past will he be able to cope with the advances and complexities tha t he encounters. But as he becomes more expert in the field, he will realize tha t something is missing from the textbooks; they necessarily omit the spirit and sense of adventure. At some stage he mus t fill this gap, for anyone who believes tha t science develops only by logical and predictable steps cannot make a good scientist, lie may be able to carry out given routines to solve particular problems, but he will be tmable to make the 'breakthrough' tha t exposes new fields and provides great opportunities. This book, then, should be read by everyone who feels tha t he has a t ta ined a modest competence in the use of X-ray diffraction. I t will show him how hal t ing were the steps of the pioneers, and should reassure him if he feels tha t he can never be as logical and precise as the textbooks pre tend tha t these pioneers were. I t shows them as people with personal difficulties and scientific doubts tha t seem extraordinary today but which were not extraordinary at the time. The production of the book coincided with the fiftieth anniversary of the discovery of the diffraction of X-rays by crysta/s. The s tory of the events leading up to this discovery is fully recounted by Ewald, who unwit t ingly p lanted the idea in Laue's mind and did not see the outcome unti l it was published. The reader will see tha t one of the most brilliant episodes in physics was not the result of careful planning but occurred because of the chance tha t the right men, the right ideas, and the right apparatus happened to be together. All tha t was needed was the catalytic action of an apparent ly unrelated problem ! Again, it is obvious to us now how the discovery should have been used: a new radiat ion was available and could be used for s tudying ma t t e r on the atomic scale; the optical principles were known and could have been used immediately. But the type of mind necessary for the discovery was not the type of mind necessary to exploit it. The subject moved from Germany to England, where the results, under the direction of W. H. and W. L. Bragg, flowed thick and fast. And so the pa t te rn of research changed, al though never again so fast as at the beginning. There were waves of progress and then apparent quietude not the s teady development described in the textbooks. Different people came into the subject for different reasons not the least impor tan t being a personal liking for a great man. The subject spread rapidly th roughout the world and is now perhaps one of the best organized subjects in the whole of science. We are indeed for tunate to have a man like Professor Ewald who, himself a pioneer, had the enthusiasm and energy to carry through the project of publishing this book. I-Ie is able to give first-hand accounts of the beginning of the subject; he is able to see the impact which the discovery made upon physics as a whole; and he has the author i ty to persuade his colleagues and his friends to contr ibute their own personal views and impressions. We should be grateful to h im for producing this mos t impor tant book. H. LIPSON