The persons who make the complaint at the head of this chapter notice that they take interest easily in certain things:  a Jack London story, a dish of ice cream, a foot-ball game.  And they take interest in them so spontaneously and effortlessly that they think these interests must be born within them.

When we examine carefully the interests of man, and trace their sources, we see that the above view is fallacious.  We acquire most of our interests in the course of our experience.  Professor James asserts:  “An adult man’s interests are almost every one of them intensely artificial; they have been slowly built up.  The objects of professional interest are most of them in their original nature, repulsive; but by their connection with such natively exciting objects as one’s personal fortune, one’s social responsibilities and especially by the force of inveterate habit, they grow to be the only things for which in middle life a man profoundly cares.”

Since interests are largely products of experience, then, it follows that if we wish to have an interest in a given subject, we must consciously and purposefully develop it.  There is wide choice open to us.  We may develop interest in early Victorian literature, prize-fight promoting, social theory, lignitic rocks, history of Siam, the collection of scarabs, mediaeval history.

We should not be deceived by the glibness of the above statements into assuming that the development of interest is an easy matter.  It requires adherence to certain definite psychological laws which we may call the laws of interest.  The first may be stated as follows:  In order to develop interest in a subject, secure information about it.  The force of this law will be apparent as soon as we analyze one of our already-developed interests.  Let us take one that is quite common—­the interest which a typical young girl takes in a movie star.  Her interest in him comes largely from what she has been able to learn about him; the names of the productions in which he has appeared, his age, the color of his automobile, his favorite novel.  Her interest may be said actually to consist, at least in part, of these facts.  The astute press agent knows the force of this law, and at well-timed intervals he lets slip through bits of information about the star, which fan the interest of the fair devotee to a still whiter heat.

The relation of information to interest is still further illustrated by the case of the typical university professor or scientist.  He is interested in certain objects of research—­infusoria, electrons, plant ecology,—­because he knows so much about them.  His interest may be said to consist partly of the body of knowledge that he possesses.  He was not always interested in the specific, obscure field, but by saturating himself in facts about it, he has developed an interest in it amounting to passionate absorption, which manifests itself in “absent-mindedness” of such profundity as to make him often an object of wonder and ridicule.