We are constantly finding results of unperceived mental processes in our consciousness. Here is a striking instance, which I borrow from a recent number of an English journal. It relates to what is considered the most interesting period of incubation in Sir William Rowan Hamilton's discovery of quaternions. The time was the 15th of October, 1843. On that day, he says in a letter to a friend, he was walking from his observatory to Dublin with Lady Hamilton, when, on reaching Brougham Bridge, he “felt the galvanic circle of thought close; and the sparks that fell from it were the fundamental relations between i, j, k,” just as he used them ever afterwards.

Still another instance of the spontaneous evolution of thought we may find in the experience of a great poet. When Goethe shut his eyes and pictured a flower to himself, he says that it developed itself before him in leaves and blossoms. The result of the mental process appeared as pictured thought; but the process itself was automatic and imperceptible.

There are thoughts that never emerge into consciousness, which yet make their influence felt among the perceptible mental currents, just as the unseen planets sway the movements of those which are watched and mapped by the astronomer. Old prejudices that are ashamed to confess themselves nudge our talking thought to utter their magisterial veto. In hours of languor, as Mr. Lecky has remarked in his “History of Rationalism,” the beliefs and fancies of obsolete conditions are apt to take advantage of us. We know very little of the contents of our minds until some sudden jar brings them to light, as an earthquake that shakes down a miser's house brings out the old stockings full of gold and all the hoards that have been hidden away in holes and crannies.

We not rarely find our personality doubled in our dreams and do battle with ourselves, unconscious that we are our own antagonists. Dr. Johnson dreamed that he had a contest of wit with an opponent, and got the worst of it: of course he furnished the wit for both. Tartini heard the Devil play a wonderful sonata and set it down on waking. Who was the Devil but Tartini himself? I remember, in my youth, reading verses in a dream, written, as I thought, by a rival fledgling of the Muse. They were so far beyond my powers that I despaired of equalling them; yet I must have made them unconsciously as I read them. Could I only have remembered them waking!

But I must here add another personal experience, of which I will say beforehand—somewhat as honest Isaak Walton said of his pike, “This dish of meat is too good for any but anglers or honest men”—this story is good only for philosophers and very small children. I will merely hint to the former class of thinkers, that its moral bears on two points: first, the value of our self-estimate, sleeping—possibly, also, waking; secondly, the significance of general formulæ when looked at in certain exalted mental conditions.

I once inhaled a pretty full dose of ether, with the determination to put on record, at the earliest moment of regaining consciousness, the thought I should find uppermost in my mind. The mighty music of the triumphal march into nothingness reverberated through my brain, and filled me with a sense of infinite possibilities, which made me an archangel for the moment. The veil of eternity was lifted. The one great truth which underlies all human experience and is the key to all the mysteries that philosophy has sought in vain to solve, flashed upon me in a sudden revelation. Henceforth all was clear: a few words had lifted my intelligence to the level of the knowledge of the cherubim. As my natural condition returned, I remembered my resolution; and, staggering to my desk, I wrote, in ill-shaped, straggling characters, the all embracing truth still glimmering in my consciousness. The words were these (children may smile; the wise will ponder): “A strong smell of turpentine prevails throughout.

My digression has served at least to illustrate the radical change which a slight material cause may produce in our thoughts, and the way we think about them. If the state just described were prolonged, it would be called insanity. I have no doubt that there are many ill-organized perhaps over-organized human brains, to which the common air is what the vapour of ether was to mine: it is madness to them to drink in this terrible burning oxygen at every breath; and the atmosphere that enfolds them is like the flaming shirt of Nessus.

The more we examine the mechanism of thought, the more we shall see that the automatic, unconscious action of the mind enters largely into all its processes. Our definite ideas are stepping-stones; how we get from one to the other, we do not know: something carries us; we do not take the step. A creating and informing spirit which is with us, and not of us, is recognized everywhere in real and storied life. It is the Zeus that kindled the rage of Achilles; it is the muse of Homer; it is the Daimon of Socrates; it is the inspiration of the seer; it is the mocking devil that whispers to Margaret as she kneels at the altar; and the hobgoblin that cried, “Sell him, sell him!” in the ear of John Bunyan: it shaped the forms that filled the soul of Michael Angelo when he saw the figure of the great Lawgiver in the yet unhewn marble, and the dome of the world's yet unbuilt basilica against the black horizon; it comes to the least of us, as a voice that will be heard; it tells us what we must believe; it frames our sentences; it lends a sudden gleam of sense or eloquence to the dullest of us all, so that, like Katterfelto with his hair on end, we wonder at ourselves, or rather not at ourselves, but at this divine visitor, who chooses our brain as his dwelling-place, and invests our naked thought with the purple of the kings of speech or song.

After all, the mystery of unconscious mental action is exemplified, as I have said, in every act of mental association. What happens when one idea brings up another? Some internal movement, of which we are wholly unconscious and which we only know by its effect. What is this action, which in Dame Quickly agglutinates contiguous circumstances by their surfaces; in men of wit and fancy, connects remote ideas by partial resemblances; in men of imagination, by the vital identity which underlies phenomenal diversity; in the man of science, groups the objects of thought in sequences of maximum resemblance? Not one of them can answer. There is a Delphi and a Pythoness in every human breast. [At Delphi in ancient Greece was the oracle of Apollo: the Pythoness was his priestess.]

The poet sits down to his desk with an odd conceit in his brain; and presently his eyes fill with tears, his thought slides into the minor key, and his heart is full of sad and plaintive melodies. Or he goes to his work saying “To-night I would have tears,” and before he rises from his table he has written a burlesque, such as he might think fit to send to one of the comic papers, if these were not so commonly cemeteries of hilarity interspersed with cenotaphs of wit and humour. These strange hysterics of the intelligence, which make us pass from weeping to laughter, and from laughter back again to weeping, must be familiar to every impressible nature; and all is as automatic, involuntary, as entirely self-evolved by a hidden organic process, as are the changing moods of the laughing and crying woman. The poet always recognizes a dictation from without, and we hardly think it a figure of speech when we talk of his inspiration.