upon a book requiring a good deal of thought.  Very frequently I would be unable to solve certain problems, but leaving them would find a day or two afterward, on taking pen in hand, that the solution traced itself without effort on the paper clearly and logically.  During the sleeping hours, or during the waking hours of a busy professional life, the brain had, without my consciousness, been solving the difficulties.  This experience is by no means a peculiar one.  Many scientific workers have borne testimony to a similar habit of the cerebrum.  The late Sir W. Rowan Hamilton, the discoverer of the mathematical method known as that of the quaternions, states that his mind suddenly solved that problem after long work when he was thinking of something else.  He says in one place:  “Tomorrow will be the fifteenth birthday of the quaternions.  They started into life or light full grown on the 16th of October, 1843, as I was walking with Lady Hamilton to Dublin and came up to Brougham Bridge; that is to say, I then and there felt the galvanic circle of thought closed, and the sparks which fell from it were the fundamental equations between I, F and K exactly as I have used them ever since.  I felt the problem to have been at that moment solved—­an intellectual want relieved which had haunted me for at least fifteen years before.”  Mr. Appolo, a distinguished scientific inventor, stated in the Proceedings of the Royal Society that it was his habit to get the bearings and facts of a case during the day and go to bed, and wake the next morning with the problem solved.  If the problem was a difficult one he always passed a restless night.  Examples might be multiplied.  Sir Benjamin Brodie, speaking of his own mental action, states that when he was unable to proceed further in some investigation he was accustomed to let the matter drop.  Then “after an interval of time, without any addition to my stock of knowledge, I have found the obscurity and confusion in which the subject was originally enveloped to have cleared away.  The facts have seemed all to settle themselves in their right places, and their mutual relations to have become apparent, although I have not been sensible of having made any distinct effort for that purpose.”

Not only is there such a thing, then, as unconscious thought, but it is probable that the best thinking is rarely, if ever, done under the influence of consciousness.  The poet creates his work when the inspiration is on him and he is forgetful of himself and the world.  Consciousness may aid in pruning and polishing, but in creating it often interferes with, rather than helps, the cerebral action.  I think any one of my readers who has done any literary or scientific writing will agree that his or her best work is performed when self and surrounding objects have disappeared from thought and consciousness scarcely exists more than it does in a dream.  Sometimes the individual is conscious of the flow of an undercurrent of mental