With respect to the "trifling exaggeration" I spoke of, allow me to explain. For the sake of clearness, I denominate the angle formed from the focal point of lens, and the glass at back of camera, the angle of delineation; the said glass the plane of delineation and the angle formed by the stereograph to the eye, the stereoscopic angle. It must be borne in mind that the stereoscopic angle is that subtended by one stereograph and the eye. I find by experiments that the angle of delineation is very often larger than the stereoscopic angle, so that the apparent enlargement spoken of by MR. SHADBOLT does not often exist; but if it did, as my vision (though excellent) is not acute enough to discover the discrepancy, I was content. I doubt not, however, under such circumstances, MR. SHADBOLT would prefer the deformities and errors proved to be present, since he has admitted that he has such preference. I leave little doubt that, if desirable, the stereoscopic angle, and that of delineation, could be generally made to agree. As to the means by which persons with two eyes, or with only one eye, judge of distance, I say not one word, that being irrelevant to this subject. But that the axes of the eyes approximate when we view objects nearer and nearer cannot be doubted, and I expressed no doubt; and it appears to me very probable that on this fact MR. SHADBOLT founds his conclusion that the cameras should radiate. This, however, ought not to be done for the reasons I have assigned. It will not do to treat the cameras as two eyes, and make them radiate because our eyes do; for it must be remembered that light entering the eyes is received on curved--whilst when it enters the cameras it falls on flat surfaces, occasioning very different results. And if this be maturely considered by MR. SHADBOLT, I believe his opinion will be greatly altered. As to the model-like appearance, I cannot yet understand exactly why it should exist; but of this I am certain, the eyes naturally do not perceive at one view three sides of a cake (that is, two sides and the front), nor two heads to a drum, nor any other like absurdity; so that I perceive no analogy between this model-like appearance and natural vision, as stated to be the case by MR. SHADBOLT. To confirm, practically, the truth of my illustrative proofs, I will send you next week some glass stereographs, to be placed at MR. SHADBOLT'S disposal, if he likes, and you will be so kind as to take charge of them. T. L. MERRITT. Maidstone. * * * * * REPLIES TO MINOR QUERIES.