This textbook is part of the Pathways in Science series, designed to meet the demands of the modern tendency to introduce science as an essential part of the elementary-school curriculum by presenting a course of carefully graded problems in science for Grades I to VI. It presents a well-balanced program, which develops elementary meanings derived from the major scientific fields--astronomy, biology, chemistry, geology, and physics. Each volume of the series has been organized about a number of units. These units present a series of problems, each of which offers a real challenge to children. Sufficient information is given in the text to lead to a satisfactory solution of the problem and to an understanding of the essential meanings that are involved in the presentation. Each unit has a page of motivating material which gives the preview to the unit and serves also to tie up unit with unit. Exercises in the form of "Things to Think About" or "Things to Do" form a basis of essential activities. The units have been so arranged that the essential meanings developed in "Our Wide, Wide World" will be utilized in later volumes of the series. Thus proper sequence is developed with an avoidance of duplication and overlapping.