This series has been prepared for use in the junior-high-school grades. The authors have been guided in this work by the recommendations set forth in the report "A Program for Teaching Science," in the Thirty-first Yearbook of the National Society for the Study of Education (1932), Part I. In this report there is a list of principles and generalizations which, taken collectively, define the major contributions of science to human welfare and to human interests. This list, with some modifications, has been used for guidance in the selection of instructional material for these books. This book is organized into relatively few teaching units, which are divided into conveniently arranged chapters. Each of these units develops understanding of some large feature of our changing environment that is definitely associated with human interest. The order in which the units are arranged in the book is such that the learner acquires, as he progresses, an increasingly enlarged understanding of the major theme of the book, that the student lives in a world of change. Reading the chapter gives to the pupil a composite picture of some situation that has in it rich potentialities for further study. The aids to learning at the end of each chapter guide the pupil to further learning through direct observation and experimentation. Ability to use the scientific method may be expected to result from practice in the use of the scientific method, especially when applied within an interesting area.