NO property of matter is more obvious, or of more continual importance, than cohesional force. These four volumes deal with many aspects of its study, and of the practical application of our knowledge. (1) Cohesion and related Problems: a General Discussion held by the Faraday Society, November 1927. Pp. 49-180 + 5 plates. (London: The Faraday Society, 1928.), 10s. 6d. net. (2) Studies in Molecular Force. By Dr. Herbert Chatley. (Griffin's Scientific Text-Books.) Pp. xi + 118. (London: Charles Griffin and Co., Ltd., 1928.) 7s. 6d. net. (3) The Viscosity of Liquids. By Emil Hatschek. (International Text-Books of Exact Science.) Pp. xii + 239. (London: G. Bell and Sons, Ltd., 1928.) 15s. net. (4) The Theory of Film Lubrication. By R. O. Boswall. Pp. xi + 280. (London, New York and Toronto: Longmans, Green and Co., Ltd., 1928.) 12s. 6d. net.