Endless books have been written about the Laws of Thought, the Nature of Thought, and the Validity of Thought. Physiologists and metaphysicians have vied with one another to tell us in twenty different ways how we think and why we think and what good our thinking may be supposed to be as affording us any real acquaintance with things in general outside our thinking-machine. One school of philosophers tells us that Thought is a secretion of the brain (_i.e._, that Thought is a form of Matter), and another that it is purely immaterial, and the only reality in the universe,—_i.e._, that Matter is a form of Thought. The meekest of men “presume to think” this, that, and the other; and the proudest distinction of the modern sage is to be a “Thinker,” especially a “free” one. But with all this much ado about Thought, it has not occurred to any one, so far as I am aware, to attempt a fair review of what any one of us thinks in the course of the twenty-four hours; what are the number of separable thoughts which, on an average, pass through a human brain in a day; and what may be their nature and proportions in the shape of Recollections, Reflections, Hopes, Contrivances, Fancies, and Reasonings. We are all aware that when we are awake a perpetual stream of thoughts goes on in “what we are pleased to call our minds,” sometimes slow and sluggish, as the water in a ditch; sometimes bright, rapid, and sparkling, like a mountain brook; and now and then making some sudden, happy dash, cataract-wise, over an obstacle. We are also accustomed to speak as if the sum and substance of all this thinking were very respectable, as might become “beings endowed with the lofty faculty of thought”; and we always tacitly assume that our thoughts have logical beginnings, middles, and endings—commence with problems and terminate in solutions—or that we evolve out of our consciousness ingenious schemes of action or elaborate pictures of Hope or Memory. If our books of mental philosophy ever obtain a place in the Circulating Libraries of another planet, the “general reader” of that distant world will inevitably suppose that on our little Tellus dwell a thousand millions of men, women, and children, who spend their existence as the interlocutors in Plato’s Dialogues passed their hours under the grip of the dread Socratic elenchus, arguing, sifting, balancing, recollecting, hard at work as if under the ferule of a schoolmaster.