The chapter headings of this book might indicate that the course has to do with physics and chemistry only. This is because general physical and chemical principles form a unifying and inclusive matrix for the mass of applications. But the examples and descriptions throughout the book include physical geography and the life sciences. Descriptive astronomy and geology have, however, been omitted. These two subjects can be best grasped in a reading course and field trips, and they have been incorporated in separate books.

The best method of presenting the principles to the children was the next problem. The study of the questions asked had shown that the children's interests were centered in the explanation of a wide variety of familiar facts in the world about them. It seemed evident, therefore, that a presentation of the principles that would answer the questions asked would be most interesting to the child. Experience with many different classes had shown that it is not necessary to subordinate these explanations of what children really wish to know to other methods of instruction of doubtful interest value.

Obviously the quantitative methods of the high school and college were unsuitable for pupils of this age. We want children to be attracted to science, not repelled by it. The assumption that scientific method can be taught to children by making them perform uninteresting, quantitative experiments in an effort to get a result that will tally with that given in the textbook is so palpably unfounded that it is scarcely necessary to prove its failure by pointing to the very unscientific product of most of our high school science laboratories.

After a good deal of experimenting with children in a number of science classes, the method followed in this book was developed. Briefly, it is as follows:

At the head of each section are several of the questions which, in part, prompted the writing of the section. The purpose of these is to let the children know definitely what their goal is when they begin a section. The fact that the questions had their origin in the minds of children gives reasonable assurance that they will to some extent appeal to children. These questions in effect state the problems which the section helps to solve.

Following the questions are some introductory paragraphs for arousing interest in the problem at hand,—for motivating the child further. These paragraphs are frequently a narrative description containing a good many dramatic elements, and are written in conversational style. The purpose is to awaken the child's imagination and to make clear the intimate part which the principle under consideration plays in his own life. When a principle is universal, like gravity, it is best brought out by imagining what would happen if it ceased to exist. If a principle is particular to certain substances, like elasticity, it sometimes can be brought out vividly by imagining what would happen if it were universal. Contrast is essential to consciousness. To contrast a condition that is very common with an imagined condition that is different brings the former into vivid consciousness. Incidentally, it arouses real interest. The story-like introduction to many sections is not a sugar coating to make the child swallow a bitter pill. It is a psychologically sound method of bringing out the essential and dramatic features of a principle which is in itself interesting, once the child has grasped it.

Another means for motivating the work in certain cases consists in first doing a dramatic experiment that will arouse the pupil's interest and curiosity. Still another consists in merely calling the child's attention to the practical value of the principle.

Following these various means for getting the pupil's interest, there are usually some experiments designed to help him solve his problem. The experiments are made as simple and interesting as possible. They usually require very inexpensive apparatus and are chosen or invented both for their interest value and their content value.

With an explanation of the experiments and the questions that arise, a principle is made clear. Then the pupil is given an opportunity to apply the principle in making intelligible some common fact, if the principle has only intelligence value; or he is asked to apply the principle to the solution of a practical problem where the principle also has utility value.