But we hold that no truth in mental philosophy is more incontestable than this, that the sight originally, and of itself, furnishes us with no knowledge of the eye, as we _now_ know that organ to exist. It does not inform us that we have an eye at all. And here we may hazard an observation, which, simple as it is, appears to us to be new, and not unimportant in aiding us to unravel the mysteries of sensation; which observation is, that, in no case whatever, does any sense inform us of the existence of its appropriate organ, or of the relation which subsists between that organ and its objects, but that the interposition of some other sense[36] is invariably required to give us this information. This truth, which we believe holds good with regard to all the senses, is most strikingly exemplified in the case of vision, as we shall now endeavour to illustrate. [36] It would not be difficult to show, that as, on the one hand, _distance_ is not involved in the original intuitions of sight, so, on the other hand, _proximity_ is not involved in the original intuitions of touch; but that, while it is the touch which establishes an interval between the organ and the objects of sight, it is the sight which establishes _no_ interval between the organ and the objects of touch. Sight thus pays back every fraction of the debt it has incurred to its brother sense. This is an interesting subject, but we can only glance at it here. Let us begin by supposing that man is a mere "power of seeing". Under this supposition, we must hold that the periphery of vision is one and the same with the periphery of visible space; and the two peripheries being identical, of course whatever objects lie within the sphere of the one must lie within the sphere of the other also. Perhaps, strictly speaking, it is wrong to say that these objects are apprehended as internal to the sight; for the conception of internality implies the conception of externality, and neither of these conceptions can, as yet, be realized. But it is obvious what the expression _internal_ means; and it is unobjectionable, when understood to signify that the Seeing Power, the Seeing Act, and the Seen Things, co-exist in a synthesis in which there is no interval or discrimination. For, suppose that we know instinctively that the seen things occupy a locality separate from the sight. But that implies that we instinctively know that the sight occupies a locality separate from them. But such a supposition is a falling back upon the notion just reprobated, that the mere act of seeing can indicate its own organ, or can localise the visual phenomena in the eye--a position which, we presume, no philosopher will be hardy enough to maintain, when called upon to do so, broadly and unequivocally. The conclusion, therefore, is irresistible, that, in mere vision, the sight and its objects cling together in a union or