To revive them easily sometimes requires practice.  For it has been discovered that all people do not naturally call up images related to the various senses with equal ease.  Most people use visual and auditory images more freely than they do other kinds.  In order to develop skill in evoking the others, practise recalling them.  Sit down for an hour of practice, as you would sit down for an hour of piano practice.  Try to recall the taste of raisins, English walnuts; the smell of hyacinths, of witch-hazel; the rough touch of an orange-skin.  Though you may at first have difficulty you will develop, with practice, a gratifying facility in recalling all varieties of images.

The third characteristic which we observed in works of the imagination is vividness.  To achieve this, pay close attention to the details of your sensory experiences.  Observe sharply the minute but characteristic items—­the accent mark on apres; the coarse stubby beard of the typical alley tough.  Stock your mind with a wealth of such detailed impressions.  Keep them alive by the kind of practice recommended in the preceding paragraph.  Then describe the objects of your experience in terms of these significant details.

We discovered, in discussing the source of imaginative works, that the men whom we are accustomed to call imaginative geniuses do not have unique communication with heaven or with any external reservoir of ideas.  Instead, we found their wonder-evoking creations to be merely new combinations of old images.  The true secret of their success is their industrious utilization of past experiences according to the program outlined above.  They select certain elements from their experiences and combine them in novel ways.  This is the explanation of their strange, beautiful and bizarre productions.  This is what Carlyle meant when he characterized genius as “the transcendent capacity for taking trouble” This is what Hogarth meant when he said, “Genius is nothing but labor and diligence.”  For concrete exemplification of this truth we need only turn to the autobiographies of great writers.  In this passage from “John Barleycorn,” Jack London describes his methods: 

“Early and late I was at it—­writing, typing, studying grammar, studying writing and all forms of writing, and studying the writers who succeeded in order to find out how they succeeded.  I managed on five hours’ sleep in the twenty-four, and came pretty close to working the nineteen waking hours left to me.”

By saying that the novel effects of imagination come by way of industry, we do not mean to imply that one should strain after novelty and eccentricity.  Unusual and happy combinations will come of themselves and naturally if one only makes a sufficient number.

There are laws of combination, known as the psychological laws of association, by which images will unite naturally.  The number of possible combinations is infinite.  By industriously making a large number, you will by the very laws of chance, stumble upon some that are especially happy and striking.