THIS enchanting and bewildering subject has in recent years been admirably expounded in two well-known books, one somewhat more severe in its treatment than the other. The author has now provided a third, which will be valued by those who already possess and take pleasure in the other two even more than by those who approach the subject for the first time. The mathematical treatment is far more severe, so much so that the average student who scoffs at the term elementary on the back of some of his text-books will certainly in this case consider it inconsistent with the subject-matter of the last few chapters. However, if he will afterwards read the subject in, say, the “Encyclopaedia Britannica,” he will realise that the term is not so misleading after all. An Elementary Treatment of the Theory of Spinning Tops and Gyroscopic Motion. By Harold Crabtree. Pp. xii + 140 and 3 plates; with illustrations. (London, New York, Bombay, and Calcutta: Longmans, Green and Co., 1909.) Price 5s. 6d. net.