We can act on our friends and neighbours in various ways, making them feel, think, accept, refuse this and that, and then observe how they act.

The differences in their action will show the differences in the feelings, etc., which we have produced.

In pursuing this method the psychologist takes a person--called the "subject" or the "re-agent"-- into his laboratory, asks him to be willing to follow certain directions carefully, such as holding an electric handle, blowing into a tube, pushing a button, etc., when he feels, sees, or hears certain things; this done with sufficient care, the results are found recorded in certain ways which the psychologist has arranged beforehand.

This second way of proceeding gives results which are gathered under the two headings "Experimental" and "Physiological Psychology." They should also have chapters in our story.
3.

There is besides another truth which the psychologist nowadays finds very fruitful for his knowledge of the mind; this is the fact that minds vary much in different individuals, or classes of individuals.