URING the last ten years the school of Logical Positivism has become fairly well known in the United States. One of the roots of this school lies in the ancient and lovely city of Vienna, from which the school (or Circle) takes its name. The Circle of is often regarded as particularly radical, and even iconoclastic, in its attitude towards traditional philosophy. Lack of appreciation of historical connections and lack of understanding of the r6le of art and religion have been described frequently as characteristics of the Vienna Circle. The present book by RICHARD VON MISES presents a quite different aspect of positivism. This doctrine is presented with its historical connections and with the affiliated ideas from all domains of human life. The author means to give a textbook of the views which are common to all positivistic groups. The reader, however, cannot help but feel that this textbook reveals in large measure the author's personality and background. R. v. MISES has worked in many fields and in many lands. He has made many original contributions to pure mathematics and mechanics; he has stimulated the engineering sciences by introducing into them the recent methods of mathematics and mathematical physics; he has given a new shape to the logical foundations of the calculus of probabilities; but-he has also been a designer of airplanes, a pilot of scouting planes, an organizer of airplane production in Austria, and an organizer of the instruction in science in Turkey. He has lived in Vienna, Strassburg, Berlin, Istanbul, and is