=The Method of Psychology.= We have enumerated the various problems of psychology, now how are they solved? The method of psychology is the same as that of all other sciences; namely, the method of observation and experiment. We learn human nature by observing how human beings act in all the various circumstances of life. We learn about the human mind by observing our own mind. We learn that we _see_ under certain objective conditions, _hear_ under certain objective conditions, _taste_, _smell_, _feel cold_ and _warm_ under certain objective conditions. In the case of ourselves, we can know both our _actions_ and our _mind_. In the case of others, we can know only their _actions_, and must infer their mental states from our own in similar circumstances. With certain restrictions and precautions this inference is legitimate. We said the method of psychology is that of observation and experiment. The experiment is observation still, but observation subjected to exact methodical procedure. In a psychological experiment we set out to provide the necessary conditions, eliminating some and supplying others according to our object. The experiment has certain advantages. It enables us to isolate the phenomena to be studied, it enables us to vary the circumstances and conditions to suit our purposes, it enables us to repeat the observation as often as we like, and it enables us to measure exactly the factors of the phenomena studied. =A Psychological Experiment.= Let us illustrate psychological method by a typical experiment. Suppose we wish to measure the individual differences among the members of a class with respect to a certain ability; namely, the muscular speed of the right hand. Psychological laboratories have delicate apparatus for making such a study. But let us see how we can do it, roughly at least, without any apparatus. Let each member of the class take a sheet of paper and a pencil, and make as many strokes as possible in a half-minute, as shown in Figure I. The instructor can keep the time with a stop watch, or less accurately with the second hand of an ordinary watch. Before beginning the experiment, the instructor should have each student taking the test try it for a second or two. This is to make sure that all understand what they are to do. When the instructor is sure that all understand, he should have the students hold their pencils in readiness above the paper, and at the signal, "Begin," all should start at the same time and make as many marks as possible in the half-minute. The strokes can then be counted and the individual scores recorded. The experiment should be repeated several times, say six or eight, and the average score for each individual recorded. [Illustration: FIGURE I.--STROKES MADE IN THIRTY SECONDS A test of muscular speed]