We are now able to follow the undulations we term light, not only into the eye, but into the brain itself, locating their central station in the occipital lobe, whence their effects radiate all over the organism. And in the case of olfaction Pawlow has taught us that its chief vegetative function, the result of radiations from the olfactory central station in the brain, is the arousing of the digestive glands to activity. The first act of digestion is olfaction. But the routes which the olfactory stimuli follow in the central nervous system and their communications with other sensory paths are not yet known. The secrets of the brain which have been disclosed to us, however wonderful they may be, concern only, we must remember, the machinery of the nervous system, that part, namely, which is of the same nature and order as the objective world, of which indeed it is a member. Hitherto have we come, but no further: “The traveller hails. The echoing walls respond. And there the matter ends. The wilds beyond Are broken rock and desert where no foot Can venture on to trace a further route, For none hath trodden or shall ever tread This hither limbus of the outer dread. Cloven abrupt, the absolute abyss Falls sheer beneath us, fathoms fathomless, And still high o’er us heaves the unclimbed hill, And the unanswered questions front us still.” The “thought” escapes us. Somewhere beyond the boundary of the physical flits this elusive, this tantalising ghost. How it is acted upon and how it reacts we know to some extent. But what the nature of its action may be is more than we can determine. Nay! A moment ago we lightly spoke of passing out of the magic circle into which we have been born, and we forthwith proceeded to talk as if we had in reality escaped from this our prison. But there is no escape for us, of course. No man can jump out of his skin. There undoubtedly are such things as “waves,” or “undulations,” or “oscillations,” or “vibrations,” or whatever we like to call them. But they are not what we imagine them to be. There is, we may suppose, a four-dimensioned universe of “space-time.” But it is beyond our conception. There is “objective reality,” in a word. But it is no reality to us. Those very expressions, glibly used though they be, are but metaphors—“pretendings” a child would call them—attempts to bring the remote a little nearer to us, to clothe the uncouth in the garments we ourselves wear; all of which is nothing but Maya—illusion—shadowplay. Let us not deceive ourselves. Along with the recent revelations of physical science there comes, say certain modern philosophers, the suspicion that the universe is irrational. At every point we are brought up short by the unknowable.