The foregoing simple study illustrates the procedure of psychology in all experimentation. A psychological experiment is an attempt to find out the truth in regard to some aspect of human nature. In finding out this truth, we must throw about the experiment all possible safeguards. Every source of error must be discovered and eliminated. In the above experiment, for example, the work must be done at the same time of day, or else we must prove that doing it at different times of day makes no difference. Nothing must be taken for granted, and nothing must be assumed. Psychology, then, is like all the other sciences, in that its method of getting its facts is by observation and experiment. SUMMARY. Science is systematic, related knowledge. Each science has a particular field which it attempts to explore and describe. The field of psychology is the study of sensitivity, action, and consciousness, or briefly, human behavior. Its main problems are development, heredity, instincts, habits, sensation, memory, thinking, and individual differences. Its method is observation and experiment, the same as in all other sciences. CLASS EXERCISES 1. Make out a list of things about human nature which you would like to know. Paste your list in the front of this book, and as you find your questions answered in this book, or in other books which you may read, check them off. At the end of the course, note how many remain unanswered. Find out whether those not answered can be answered at the present time. 2. Does everything you do have a cause? What kind of cause? 3. Human nature is shown in human action. Human action consists in muscular contraction. What makes a muscle contract? 4. Plan an experiment the object of which shall be to learn something about yourself. 5. Enumerate the professions and occupations in which a knowledge of some aspect of human nature would be valuable. State in what way it would be valuable. 6. Make a list of facts concerning a child, which a teacher ought to know. 7. Make a complete outline of Chapter I. REFERENCES FOR CLASS READING MÜNSTERBERG: _Psychology, General and Applied_, Chapters I, II, and V. PILLSBURY: _Essentials of Psychology_, Chapter I. PYLE: _The Outlines of Educational Psychology_, Chapter I. TITCHENER: _A Beginner's Psychology_, Chapter I. CHAPTER II DEVELOPMENT OF THE RACE AND OF THE INDIVIDUAL