MERRITT will object that an erroneous effect is produced; if he will refer to my statement (Vol. viii., p. 228.), he will find that it is precisely what I admitted; and he appears to have overlooked the _proviso_ attached to my next observation (judging by his comment thereon), so I shall make no farther remark upon that point, beyond inquiring why the defect he is content to put up with is called a _trifling exaggeration_, while that which is less offensive to me is designated as _absolute deformity_ and error? Persons with one eye are _not good judges_ of distance, and this may be easily tested thus:--Close one eye, and endeavour to dip a pen in an inkstand at some little distance not previously ascertained by experiment, with both eyes open; it will be found far less easy than would be imagined. One-eyed people, from habit, contrive to judge of distance mainly by _relative position_, and by moving the head _laterally_ cause a change therein: to them, all pictures are, to an extent, stereoscopic. I am really amazed that my advocacy of the radial, instead of the parallel, position of the cameras should have been so misunderstood. Surely, it cannot be seriously asserted that the former will produce _two_ vanishing points, and the latter only one? And as to the supposition connected with the boy, the ass, and the drum, a camera that would produce the effect of showing both sides of the ass, both legs of the boy, and both heads of the drum, _with a movement of only 2-1/2 inches_, whether radially or parallel, would indeed be a curiosity. But if the motion of the camera extended over a space sufficiently large to exhibit the phenomena alluded to, then it would confirm what I have before advanced, viz. present the idea of a _small model_ of the objects, which could be so placed as to show naturally these very effects.