In general, it is better to spread the repetitions over a period of time.  The question then arises, what is the most effective distribution?  Various combinations are possible.  You might rehearse the poem once a day during the month, or twice a day for the first fifteen days, or the last fifteen days, four times every fourth day, ad infinitum.  In the face of these possibilities is there anything that will guide us in distributing the repetitions?  We shall get some light on the question from an examination of the curve of forgetting—­a curve that has been plotted showing the rate at which the mind tends to forget.  Forgetting proceeds according to law, the curve descending rapidly at first and then more slowly.  “The larger proportion of the material learned is forgotten the first day or so.  After that a constantly decreasing amount is forgotten on each succeeding day for perhaps a week, when the amount remains practically stationary.”  This gives us some indication that the early repetitions should be closer together than those at the end of the period.  So long as you are forgetting rapidly you will need more repetitions in order to counterbalance the tendency to forget.  You might well make five repetitions; then rest.  In about an hour, five more; within the next twenty-four hours, five more.  By this time you should have the poem memorized, and all within two days.  You would still have fifteen repetitions of the thirty, and these might be used in keeping the poem fresh in the mind by a repetition every other day.

As intimated above, one important principle in memorizing is to make the first impressions as early as possible, for older impressions have many chances of being retained.  This is evidenced by the vividness of childhood scenes in the minds of our grandparents.  An old soldier recalls with great vividness events that happened during the Civil War, but forgets events of yesterday.  There is involved here a principle of nervous action that you have already encountered; namely, that impressions are more easily made and retained in youth.  It should also be observed that pathways made early have more chances of being used than those made recently.  Still another peculiarity of nervous action is revealed in these extended periods of memorizing.  It has been discovered that if a rest is taken between impressions, the impressions become more firmly fixed.  This points to the presence of a surprising power, by which we are able to learn, as it were, while we sleep.  We shall understand this better if we try to imagine what is happening in the nervous system.  Processes of nutrition are constantly going on.  The blood brings in particles to repair the nerve cells, rebuilding them according to the pattern left by the last impression.  Indeed, the entrance of this new material makes the impression even more fixed.  The nutritional processes seem to set the impression much as a hypo bath fixes or sets an impression on a photographic plate.