Similarly we find cases where the uprush of subliminal faculty is concerned with the deep organic sensation of muscular resistance. We need not postulate any direct or supernormal knowledge,--but merely a subliminal calculation, such as we see in the case of "arithmetical prodigies," expressing itself supraliminally, sometimes in a phantasmal picture, sometimes as a mere "conviction," without sensory clothing.[31] Passing on here to subliminal products of _visual_ type, I am glad to be able to quote the following passage which seems to me to give in germ the very theory for which I am now contending on the authority of one of the most lucid thinkers of the last generation. The passage occurs in an article by Sir John Herschel on "Sensorial Vision," in his _Familiar Lectures on Scientific Subjects_, 1816. Sir John describes some experiences of his own, "which consist in the involuntary production of visual impressions, into which geometrical regularity of form enters as the leading character, and that, under circumstances which altogether preclude any explanation drawn from a possible regularity of structure in the retina or the optic nerve."[32] Twice these patterns appeared in waking daylight hours,--with no illness or discomfort at the time or afterwards. More frequently they appeared in darkness; but still while Sir John was fully awake. They appeared also twice when he was placed under chloroform; "and I should observe that I never lost my consciousness of being awake and in full possession of my mind, though quite insensible to what was going on.... Now the question at once presents itself--What _are_ these Geometrical Spectres? and how, and in what department of the bodily or mental economy do they originate? They are evidently not dreams. The mind is not dormant, but active and conscious of the direction of its thoughts; while these things obtrude themselves on notice, and by calling attention to them, _direct_ the train of thought into a channel it would not have taken of itself.... If it be true that the conception of a regular geometrical pattern implies the exercise of thought and intelligence, it would almost seem that in such cases as those above adduced we have evidence of a _thought_, an intelligence, working within our own organisation distinct from that of our own personality." And Sir John further suggests that these complex figures, entering the mind in this apparently arbitrary fashion, throw light upon "the suggestive principle" to which "we must look for much that is determinant and decisive of our volition when carried into action." "It strikes me as not by any means devoid of interest to contemplate cases where, in a matter so entirely abstract, so completely devoid of any moral or emotional bearing, as the production of a geometrical figure, we, as it were, seize upon that principle in the very act, and in the performance of its office."