The sense at the bottom of any scientific study is curiosity. When man is curious about an event he observes, he will ask himself questions such as Why, What for, and How, and try to find somewhat uncertain answers to those questions in order to suppress that sense. Then, he will design experiments to generate more satisfactory replies to his observation. Designing an experiment and conducting that designed experiment are the sine qua non of any scientific study. In the light of numerous experiments conducted, a model that can explain the observation is introduced. This model may be supported and improved, if necessary, through other experiments, or invalidated totally with another model in the course of time. The entire process described in this part constitutes the frame of the scientific method. The scientists are the people who operate this process.