A BOOK entitled "Origins of Clerk Maxwell's Electric Ideas as described in Familiar Letters to William Thomson" has been published by the Cambridge University Press (price 3s. 6d.) These letters cover the period 1854–79 and illustrate clearly the genesis and rapid progress of Clerk Maxwell's ideas as he groped his way towards a structural theory of the electric and magnetic field. Some of the questions he asks Thomson are by no means easy to answer. In his first letter (Feb. 1854) he asks: "Suppose a man to have a popular knowledge of electrical show experiments and a little antipathy to Murphy's Electricity, how ought he to proceed in reading and working so as to get a little insight into the subject which may be of use to him in further reading?" In subsequent letters he continues to ask still more intricate questions, so doubtless Thomson's answers must have been satisfactory. In another letter he says, "I do not know the game laws and patent laws of science . . . but I certainly intend to poach among your electrical images". He fully appreciates Thomson's problem of an electrified spherical bowl. "Your bowl investigations are first-rate. I must find the induction through a round hole in a plate by means of them. Whether would you have me bag the whole thing for my book, or give results and references with an account of the method?" The letters given in this book were originally printed in Part 5 of vol. 32 of the Proceedings of the Cambridge Philosophical Society. As they will be of interest to many mathematical physicists, the Cambridge Press did well to publish them. Sir Joseph Larmor has edited the book.