IN Goethe's “Maximen und Reflexionen” there occurs the passage: “Versuche deine Pflicht zu tun, und du weisst sogleich was an dir ist. Was aber ist deine Pflicht? Die Forderung des Tages.” The author of the present volume tells us that this passage expresses the spirit in which he has from time to time, particularly during the last few years, attempted the solution of problems quite outside the sphere of his original scientific activity. These problems cropped up in the course of the day's work, and, so far as the author was personally concerned, imperatively demanded a solution. The numerous articles and speeches here collected represent Prof. Ostwald's views on the most varied questions, such as personality, immortality, the relation of art and science, the theory of happiness, science and technology, duelling, international languages, and educational reform. These and many other topics are discussed in a highly stimulating manner, the originality of the author's argument being equalled only by the charm of his style and the wealth of illustration which he has at his disposal. If one accepts the definition of a professor as given by “Fliegende Blätter”—“der Professor ist ein Mann welcher anderer Meinung ist”—it may readily be granted that the author, with his refreshing novelty of view, has fully earned the title.