Page:Ferrier's Works Volume 3 "Philosophical Remains" (1883 ed.).djvu/376

366 distance of objects. That knowledge must be directly given in the very function and exercise of vision, as every one will admit, without going to the expense of an octavo volume to have it proved.

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 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.

Let us begin by supposing that man is a mere "power of seeing." Under this supposition, we must