lens and cornea; but if we increase the refraction by substituting the convexity of the magnifying glass for that of the lens and cornea, we then obtain a clear image of objects even when they are as near as half an inch from our eyes. Objects thus seen in close proximity to us and in the size corresponding to that proximity, are transferred by our Understanding to the distance at which we naturally see distinctly, i.e. to about eight or ten inches from our eyes, and we then estimate their magnitude according to this distance and to the given visual angle.
I have entered thus fully into detail concerning all the different processes by which seeing is accomplished, in order to show clearly and irrefragably that the predominant factor in them is the Understanding, which, by conceiving each change as an effect and referring that effect to its cause, produces the cerebral phenomenon of the objective world on the basis of the à priori fundamental intuitions of Space and Time, for which it receives merely a few data from the senses. And moreover the Understanding effects this exclusively by means of its own peculiar form, the law of Causality; therefore quite directly and intuitively, without any assistance whatever from reflection—that is, from abstract knowledge by means of conceptions and of language, which are the materials of secondary knowledge, i.e. of thought, therefore of Reason.
That this knowledge through the Understanding is independent of Reason's assistance, is shown even by the fact, that when, at any time, the Understanding attributes a given effect to a wrong cause, actually perceiving that cause, whereby illusion arises, our Reason, however clearly it may recognise in abstracto the true state of the matter, is nevertheless unable to assist the Understanding, and the illusion persists undisturbed in spite of that better knowledge. The above-mentioned phenomena of seeing and feeling double, which result from an abnormal position
