to determine that visible objects are external, or at any distance at all from the eye: the other opinion is, that sight, though gifted with the capacity of determining that all visible objects are at some distance from the eye, is yet unable to determine the relative distances at which they stand towards it and towards one another. In the words of Mr Bailey, "Whether objects are seen to be external, or at some distance, is one question altogether distinct from the inquiry—whether objects are seen by the unassisted vision to be at different distances from the percipient." He then adds, "yet Berkeley uniformly assumes them to be the same, or, at least, takes it for granted that they are to be determined by the same arguments." This is true enough in one sense, but Mr Bailey should have considered, that if Berkeley did not make the discrimination, it was because he conceived that the opinion which maintained the absolute non-externality of visible objects, i.e., of objects in relation to the organ of sight, was the only question properly at issue. The remark, however, is valuable, because Berkeley's followers, Reid, Stewart, and others, have supposed that the other question was the one to be grappled with; and, accordingly, they have not ventured beyond maintaining that the eye is unable to judge of the different degrees of distance at which objects may be placed from it. But the thoroughgoing opinion is the true one, and the followers have deserted their leader only to err, or to discover truths of no scientific value or significance whatever.
Let us now consider the general object which Berkeley had in view, and determine the proper point of sight from which his "theory of vision" should be regarded. We have already remarked that it was but the stepping-stone or prelude to those maturer and more extended doctrines of idealism in which his genius afterwards expatiated, and which have made his name famous throughout every corner of the philosophic world; and which we have endeavoured to do justice to in the preceding pages, giving a more enlarged and unobjectionable construction to their principle, and clearing, we think, at least some of the difficulties which beset his statement of it. His theory of vision may be called an essay on the idealism of the eye, and of the eye alone. It is idealism restricted to the consideration of this sense, and is the first attempt that ever was made to embody a systematic and purely speculative critique of the facts of seeing. We use the words purely speculative in contradistinction from geometrical and physiological critiques of the same sense; of which there were abundance in all languages, but which, proceeding on mathematical or anatomical data, which are entirely tactual, had, in Berkeley's opinion, nothing whatever to do with the science of optics, properly so called. Optics, as hitherto treated, that is to say, as established on mathematical principles, appeared to him to be a false science of vision; for this reason, that the blind were found to be just as capable of understanding and appreciating it, as those were who could see. Hence he concluded, and most justly, that the true facts of sight had been left out of the estimate, because these were, and necessarily must be, facts which no blind person could form any conception of. He accordingly determined to construct, or at least to pave the way towards the construction of, a truer theory of vision, in which these—the proper and peculiar facts of the sense—should be taken exclusively into account: and hence, passing from the mathematical and physiological method, he took up a different, and what we have called a purely speculative ground—a ground which cannot be rendered intelligible or conceivable to the blind, inasmuch as they are deficient in the sense which alone furnishes the data that are to be dealt with. The test by which Berkeley tried optical science was—can the blind be brought to understand, or to form any conception of it? If they can, then the science must be false, for it ought to be a science of experiences from which they are entirely debarred. We should bear in mind then, first of all, that his object in constructing his theory of vision was, leaving all geometrical and anatomical considerations out of the question, to apprehend the proper and peculiar facts of sight—the facts, the whole facts, and nothing but the facts, of that particular and isolated sense.
Now we think that Mr Bailey's leading error consists in his not having remarked the unswerving devotedness with which Berkeley follows out this aim; and hence, having failed to appreciate the singleness and unrelaxing perseverance of his purpose, he has consequently failed to appreciate the
