THE issue by the Science Museum of Books 2 and 3, describing the exhibits and outlining the lectures delivered at the special exhibition devoted to this subject in the Science Museum from March until June last year, completes the account of the exhibition. The three books have been edited by Mr. T. C. Crawhall, with the assistance of Dr. O. Kantorowicz for Book 2. The first book, issued at 6d., gives a survey of physical principles and some applications ; the second, issued at 2s., deals with the apparatus exhibited for temperature reduction, temperature and pressure measurement, liquefaction and solidification of gases, the properties of the products, their storage and their applications. Included in the methods of cooling is that of demagnetizing a paramagnetic material. The third book, issued at Is. 3d., gives accounts of the development of low-temperature technique, by Prof. M. Travers, the industrial uses of low temperatures, by Messrs. C. G. Bainbridge, J. T. Randall and I. J. Faulkner respectively, and the approach to the absolute zero, by Dr. J. D. Cockroft, Prof. F. Linde-man and Prof. F. Simon respectively. The three books constitute a valuable record of the present position of a subject which promises to have many applications in industry.