IN his introduction to a set of pamphlets on recent developments in physics (“Exposés de physique théorétique”) published by Hermann et Cie, of Paris (6 francs each), Prof. L. de Broglie raises once more the question of how contact can be maintained between workers at different branches of physics. It is now quite impossible for any one person both to read critically all new papers, in any but a most limited field, and to advance the subject himself. Realisation of this is, of course, not new, and has inspired, amongst other publications, the American Physical Society's Reviews of Modern Physics. The present series seems likely, however, to fulfil its purpose better than anything that has gone before. Although definitely for advanced workers, the articles are anything but abstracts, being well written and critical, and containing adequate detail without providing what is really irrelevant to anyone not a specialist in the particular subject dealt with. They also deal with relatively new or very recent work. Of the two at present under notice, Prof. de Broglie's is based on Landau and Peierl's treatment of the uncertainty principle (Z. Phys., vol. 69, p. 56), and is purely theoretical. The other, by Irène Curie and F. Joliot, is an account of the neutron experiments, particularly those done by the workers in Paris; it contains an interesting set of reproductions of Wilson cloud trails, which supplement those recently published by Feather and Dee in the Proceedings of the Royal Society. Each article occupies a little more than twenty pages, and although attractively presented, is certainly cheap.