knowledge of the brain leaves us with regard to the origin of the lowest mental phenomena, and the complete solution of the highest problems of the physical world which we get from such knowledge. A brain that should, from one cause or another, be unconscious — for instance, one that should sleep without dreaming — would, had we astronomical knowledge of it, hold no secret; and, if we possessed astronomical knowledge of the rest of the body also, then the whole human machine, with its respiration, its heart-beats, its exchanges of materials, its heat, etc. — in short, every thing short of the essence of matter and force, would be fully deciphered. The dreamless sleeper is comprehensible to us, like the universe previous to consciousness. But, as, on the first awakening of consciousness, the world became doubly incomprehensible, so too is it with the sleeper, at the first appearance of a faint image in dreaming.
The irreconcilable conflict of the mechanical view of the universe with freedom of will, and hence indirectly with ethics, is no doubt a matter of high importance. The ingenuity of thinkers in all times has been exhausted in trying to reconcile them, and this question will afford exercise to the mind of man forever. To say nothing of the fact that free-will may be denied, whereas pleasure and pain are unquestionable; desire, which gives the impetus to exertion, and hence gives occasion to act, or not to act, is necessarily preceded by sense-impressions. Hence it is to the problem of sensation, and not, as I have once said, to that of free-will, that analytical mechanics leads.
And here is the other limit of our knowledge of Nature. It is no less absolute than the first limit. For two thousand years, despite all the advances made by natural science, mankind has made no substantial progress toward the understanding of matter and force, any more than toward the understanding of mental activity from its material conditions. And so will it ever be. Even the Mind imagined by Laplace, with its universal formula, would, in its efforts to overstep these limits, be like an aëronaut essaying to reach the moon. In its world of mobile atoms, the cerebral atoms are in motion indeed, but it is a dumb show. This Mind views their hosts, and sees them crossing each other's course, but does not understand their pantomime; they think not for him, and hence, as we have already seen, the world of this Mind is still meaningless.
In this Mind we have the measure of our own capacity, or rather our impotence. Our knowledge of Nature is thus shut up between two limits, the one forevermore determining our incapacity to comprehend matter and force, the other determining our inability to understand mental facts from their material conditions. Between these limits the man of science is lord and master; he dismembers and builds up, and no one durst say wherein his knowledge and his power are circumscribed. Beyond these limits he cannot now, nor can he ever, go.