o say
that it never maintains a constant level of concentration for any
considerable length of time, but regularly ebbs and flows. The
explanation of this rhythmic action would take us too far afield at this
point. When we remember, however, that our entire organism works within
a great system of rhythms--hunger, thirst, sleep, fatigue, and many
others--it is easy to see that the same law may apply to attention. The
rhythms of attention vary greatly, the fluctuations often being only a
few seconds apart for certain simple sensations, and probably a much
greater distance apart for the more complex process of thinking. The
seeming variation in the sound of a distant waterfall, now loud and now
faint, is caused by the rhythm of attention and easily allows us to
measure the rhythm for this particular sensation.

4. POINTS OF FAILURE IN ATTENTION

LACK OF CONCENTRATION.--There are two chief types of inattention whose
danger threatens every person. _First_, we may be thinking about the
right things, but not thinking _hard_ enough. We lack mental pressure.
Outside thoughts which have no relation to the subject in hand may not
trouble us much, but we do not attack our problem with vim. The current
in our stream of consciousness is moving too slowly. We do not gather up
all our mental forces and mass them on the subject before us in a way
that means victory. Our thoughts may be sufficiently focused, but they
fail to "set fire." It is like focusing the sun's rays while an eclipse
is on. They lack energy. They will not kindle the paper after they have
passed through the lens. This kind of attention means mental dawdling.
It means inefficiency. For the individual it means defeat in life's
battles; for the nation it means mediocrity and stagnation.

A college professor said to his faithful but poorly prepared class,
"Judging from your worn and tired appearance, young people, you are
putting in twice too many hours on study." At this commendation the
class brightened up visibly. "But," he continued, "judging from your
preparation, you do not study quite half hard enough."

Happy is the student who, starting in on his lesson rested and fresh,
can study with such concentration that an hour of steady application
will leave him mentally exhausted and limp. That is one hour of triumph
for him, no matter what else he may have accomplished or failed to
accomplish during the time. He can afford an occasional pause for rest,
for difficu