THE subject of the heat treatment of steel is one which during recent years has received a large amount of attention, and the results of numerous researches in England, on the Continent, and in America have been published before various technical societies. These have, however, for the most part dealt with special branches of the subject, largely from the theoretical point of view, and comparatively little has been published by men who have had to deal with the application of the various theories in their daily practice. The Heat Treatment of Tool Steel: an Illustrated Description of the Physical Changes and Properties Induced in Tool Steel by Heating and Cooling Operations. By Harry Brearley. Pp. xvii + 160. (London: Longmans, Green and Co., 1911.) Price 10s. 6d. net.