XV. Commercial Fertilizers. XVI. Farm Manure. XX. Milk and Its Products. XXI. Poisons for Farm and Orchard Pests. * * * * * THE MACMILLAN COMPANY 64-66 FIFTH AVENUE BOSTON NEW YORK CITY DALLAS CHICAGO ATLANTA SAN FRANCISCO Practical Physics By N. HENRY BLACK of the Roxbury Latin School Boston, and Professor HARVEY N. DAVIS of Harvard University. _Cloth, 12mo, illustrated, 488 pages. List price, $1.25_ “In preparing this book,” say the authors in the Preface, “we have tried to select only those topics which are of vital interest to young people, whether or not they intend to continue the study of physics in a college course. “In particular, we believe that the chief value of the informational side of such a course lies in its applications to the machinery of daily life. Everybody needs to know something about the working of electrical machinery, optical instruments, ships, automobiles, and all those labor-saving devices, such as vacuum cleaners, fireless cookers, pressure cookers, and electric irons, which are found in many American homes. We have, therefore, drawn as much of our illustrative material as possible from the common devices in modern life. We see no reason why this should detract in the least from the educational value of the study of physics, for one can learn to think straight just as well by thinking about an electrical generator, as by thinking about a Geissler tube.... “To understand any machine clearly, the student must have clearly in mind the fundamental principles involved. Therefore, although we have tried to begin each new topic, however short, with some concrete illustration familiar to young people, we have proceeded, as rapidly as seemed wise, to a deduction of the general principle. Then, to show how to make use of this principle, we have discussed other practical applications. We have tried to emphasize still further the value of principles, that is, generalizations, in science, by summarizing at the end of each chapter the principles discussed in that chapter. In these summaries we have aimed to make the phrasing brief and vivid so that it may be easily remembered and easily used.” The new and noteworthy features of the book are the admirable selection of familiar material used to develop and apply the principles of physical science, the exceptionally clear and forceful exposition, showing the hand of the master teacher, the practical, interesting, thought-provoking problems, and the superior illustrations.