thing in question.  Of course, the minute you begin thinking, new associations, images, memories, come flocking in, and the attention occupies itself with each in turn.  All may concern the idea with which you started out, but the very fact that these have been added to the mental content of the instant makes the percept of ink blot or the concept of bravery different from the bare thing with which the attention began.  If this change and fluctuation of the mental state does not take place, the attention flits to something else.  The length of time that the attention may be engaged with a topic will depend, then, upon the number of associations connected with it.  The more one knows about a topic, the longer he can attend to it.  If it is a new topic, the more suggestive it is in calling up past experience or in offering incentive for experiment or application, the longer can attention stay with it.  Such a topic is usually called “interesting,” but upon analysis it seems that this means that for one of the above reasons it develops or changes and therefore holds the attention.  This duration of attention will vary in length from a few seconds to hours.  The child who is given a problem which means almost nothing, which presents a blank wall when he tries to attend to it, which offers no suggestions for solution, is an illustration of the first.  Attention to such a problem is impossible; his attention must wander.  The genius who, working with his favorite subject, finds a multitude of trains of thought called up by each idea, and who therefore spends hours on one topic with no vacillation of attention, is an illustration of the second.

Attention has been classified according to the kind of feeling which accompanies the activity.  Sometimes attention comes spontaneously, freely, and the emotional tone is that accompanying successful activity.  On the other hand, sometimes it has to be forced and is accompanied by feelings of strain and annoyance.  The first type is called Free[2] attention; the second is Forced attention.

Free attention is given when the object of attention satisfies a need; when the situation attended to provides the necessary material for some self-activity.  The activity of the individual at that second needs something that the situation in question gives, and hence free, spontaneous attention results.  Forced attention is given when there is a lack of just such feeling of need in connection with the object of attention.  It does not satisfy the individual—­it is distinct from his desires at the time.  He attends only because of fear of the results if he does not, and hence the condition is one of strain.  All play takes free attention.  Work which holds the worker because it is satisfying also takes free attention.  Work which has in it the element of drudgery needs forced attention.  The girl making clothes for her doll, the boy building his shack in the woods, the inventor working over his machine, the student