THIS is a very good specimen of that sort of book which is an amplification of the lecture notes of a professor who has carefully prepared problems for students. We may not always like the way in which he introduces the subject to his pupils, and we may say that it is unphilosophical and even cryptic, and sometimes too brilliant, but such comments are often due to the fact that his way happens not to be the usual way of presenting the subject. The way of Prof. Reeve probably suits his particular class of unscientific pupils very well. He uses terms in senses somewhat different from those in common use. He is absolutely correct in many statements with which we would willingly find as much fault as Macaulay did with those of Robert Montgomery. For example:— The Thermodynamics of Heat Engines. By Sidney A. Reeve, Professor of Steam-Engineering at the Worcester Polytechnic Institute (U.S.A.). Pp. xiv + 316 + 42. (New York: The Macmillan Company; London: Macmillan and Co., Ltd., 1903.) Price 10S. 6d. net.