TIMES change. Before the war, what was missing from the American scene was "a good five-cent cigar." One of the Gods of the present generation is Science, and the efforts of Wells, Durant Eddington, Jeans, and others to explain what the new theoretical science means left unsatisfied the persistent statement that "what this country needs is a good two-dollar explanation of Relativity.

"The Evolution of Physics" costs fifty cents more than that amount and is worth to the reader a king's ransom, if there could be valued in money the stimulation and pleasure of a journey in pure reason toward an understanding of matter and space. It is not an easy book to read. Though mathematical formulae are completely left out and the words are short and there are many illustrations and metaphors, the subject matter is inherently difficult. Einstein, of course, can be expected to understand his own theory more clearly than any of his popularizers, and much more clearly than they can he explain the ideas to the laymen. Nevertheless a good deal of concentration is required to follow each step in the thought, and a good understanding of the content must require several rereadings. One of the most pleasant features of the book is the absence of any dramatization of the subject or of any sentimental speculation about the connection between physics and a mathematical God.

Much of the clarity of the book lies in the method of approach to the problem of physics. The Mechanical Explanation of nature occupies the opening chapters, and how it was devised by Aristotle, Galileo, Newton, and others to account for phenomena as they saw them. Next is detailed the new facts about light and magnetics, and its replacement by the current theories of four dimensions, quanta, relativity, and the time-space continuum. Each problem is outlined as it arises in a logical approach, and each theory gets its day in court, with the difficulties that led to its formation, the events it explains, and the new difficulties that lead to its revision and rejection.

Dr. Einstein believes that Physics is in a bad dilemma at present, with one leg in the Field Theory and the other buried in Quanta. Investigation into particles of matter leads from descriptions of events in time and space to probability waves, and the problem of placing such waves in the field concept of space is a major one. Suppose that a solution is found; in what way are we better off? Dr. Einstein is not sure. "In our endeavor to understand reality we are somewhat like a man trying to understand the mechanism of a closed watch. He sees the face and the moving hands, even hears its ticking, but he has no way of opening the case. If he is ingenious he may form some picture of a mechanism which could be responsible for all the things he observes, but he may never be quite sure his picture is the only one which could explain his observations. He will never be able to compare his picture with the real mechanism and he cannot even imagine the possibility or the meaning of such a comparison."