That the axes of the eyes are inclined when viewing objects, is readily proved thus:--Let a person look across the road at any object--say a shop-window; but stand so that a _lamp-post near him_ shall intervene, and be in a _direct line_ between the observer's nose and the object viewed. If he be requested to observe the post instead of the distant object, the pupils of his eyes will be seen to approach one another; and on again looking to the distant object, will instantly recede. The _range_ of vision is another point that appears to be misunderstood, as we are differing about words instead of facts. The column is an illustration that will _exactly_ suit my views; for I call the _range_ of vision the same if taken from side to side of the column, although it is perfectly true that the tangents to the two eyes differ by the angle they subtend: but certainly MR. WILKINSON'S case (Vol. viii., p. 181.) of seven houses and five bathing-machines in one picture, and five houses and eight machines in the other, illustrates an instance where the range of vision is not the same; but I contend that the stereoscopic effect is then _confined_ to five {349} houses and five machines, otherwise MR. WILKINSON'S supposititious case (_ibid._), of all machines in one, and all houses in the other, might be considered as stereoscopic. In concluding this very lengthened and, I fear, tedious reply, I beg to assert that I am most willing to recant any proposition I may have put forth, if _proved_ to be erroneous; but I must have proof, not mere assertion. And farther, my willing thanks are always tendered to any one kind enough to correct an error. GEO. SHADBOLT. _Mr. Pumphrey's Process for securing black Tints in Positives._--The importance that appears to be attached by some of thy correspondents to the stereoscopic appearance of photographs, induces me to call the attention of those who may not have noticed it to the fact that, as all camera pictures are monocular, they are best seen by closing one eye, and then they truly represent nature; and the effect of distance (which so often appears wanting in photographs) is given with marvellous effect, so well indeed as to render the use of a stereoscope unnecessary. Like other photographers, I have been long seeking for a method, easy, cheap, and certain, for obtaining the black tints that are so highly prized by many in the French positives; and having at last attained the object of my search, I lose no time in laying it before my fellow-operators.