There is another misunderstanding into which my opponent has fallen, viz. the part of the object to be delineated, which should form the centre of radiation, is not the most contiguous visible point, but the most remote principal point of observation. I perceive that this is the case from two illustrations he was kind enough to forward me, being stereographs of a [T-square] square, placed with the points of junction towards the observer, and the tail receding from him; and in one case the angle of the square is made the centre of radiation, and while its distance from the camera is only six feet, the points of delineation are no less than three feet apart. To push an argument to the extreme to test its value, is quite right; but this goes far beyond the extreme, if I may be allowed such a very Hibernian expression. No object, however minute, can be clearly seen if brought nearer to the eyes than a certain point, because it will be what is technically called out of focus. It is true that this point differs in different individuals, but the _average distance_ of healthy vision is 10 inches. Now, adopting MR. MERRITT'S own standard of 2-1/2 inches between the eyes, it is clear that supposing the central point had been rightly selected, the distance between the cameras was _only double_ what might have been taken an extreme distance. It is scarcely necessary to suggest what a person devoid of taste (in which category I am no doubt included) might do in producing monstrosities by adopting the radial method, as such an one is not very likely to produce good results at all. I now address myself to another accusation. It is quite true that I am unacquainted with the _scholastic dogmas_ of perspective, but equally true that I am familiar with _the facts_ thereof, as any one must be who has studied optical and geometrical science generally; and while I concur in the propositions as enunciated for a one-eyed picture, I by no means agree to the assumption that the "vanishing points," in the two stereographs taken radially with the necessary precautions, "would be so far apart, that they could not in the stereoscope flow into one;" on the contrary, direct experiment shows me, what reason also suggests, that they do flow into one as _completely as in nature when viewed by both eyes_. I put the proposition thus, because I do not hesitate to avow that in nature, as interpreted by binocular vision, these points do not _absolutely_, but only approximately, flow _into one_; otherwise one eye would be as effective as two. I have not the smallest objection to my views being considered "false to art," as, alas! her fidelity to nature is by no means beyond suspicion. {477}