Hamilton and other writers have compared the mind's action to that of a row of billiard balls, of which one is struck and the impetus transmitted throughout the entire row, the result being that only the last ball actually moves, the others remaining in their places. The last ball represents the conscious thought--the other stages in the unconscious mentation. Lewes, speaking of this illustration, says: "Something like this, Hamilton says, seems often to occur in a train of thought, one idea immediately suggesting another into consciousness--this suggestion passing through one or more ideas which do not themselves rise into consciousness. This point, that we are not conscious of the formation of groups, but only of a formed group, may throw light on the existence of unconscious judgments, unconscious reasonings, and unconscious registrations of experience." Many writers have related the process by which the unconscious mentation emerges gradually into the field of consciousness, and the discomfort attending the process. A few examples may prove interesting and instructive. Maudsley says: "It is surprising how uncomfortable a person may be made by the obscure idea of something which he ought to have said or done, and which he cannot for the life of him remember. There is an effort of the lost idea to get into consciousness, which is relieved directly the idea bursts into consciousness." Oliver Wendell Holmes said: "There are thoughts that never emerge into consciousness, and which yet make their influence felt among the perceptive mental currents, just as the unseen planets sway the movements of the known ones." The same writer also remarks: "I was told of a business man in Boston who had given up thinking of an important question as too much for him. But he continued so uneasy in his brain that he feared he was threatened with palsy. After some hours the natural solution of the question came to him, worked out, as he believed, in that troubled interval." Dr. Schofield mentions several instances of this phase of the workings of the unconscious planes of the mind. We mention a couple that seem interesting and to the point: "Last year," says Dr. Schofield, "I was driving to Phillmore Gardens to give some letters to a friend. On the way, a vague uneasiness sprang up, and a voice seemed to say, 'I doubt if you have those letters.' Conscious reason rebuked it, and said, 'Of course you have; you took them out of the drawer specially.' The vague feeling was not satisfied, but could not reply. On arrival I found the letters were in none of my pockets. On returning I found them on the hall table, where they had been placed a moment putting on my gloves."