"_The Stereoscope considered in relation to the Philosophy of Binocular Vision_" is the title of a small pamphlet written by a frequent contributor to this journal, Mr. C. MANSFIELD INGLEBY, in which he has "attempted to sketch out such modifications of the theory of double vision as appear to him to be entailed on the rationale of the stereoscope." The corroboration thus indirectly afforded to the principles of Sir William Hamilton's _Philosophy of Perception_ has induced MR. INGLEBY to dedicate his word to that distinguished metaphysician. The essay will, we have no doubt, be perused with great interest by many of our photographic friends, for whose gratification we shall borrow its concluding paragraph. "In conclusion we must not forget to acknowledge our obligations to the photographic art, not merely as one of the most suggestive results of natural science, but as a means of the widest and soundest utility. To antiquaries the services of photography have a unique value, for, by perpetuating in the form of negatives those monuments of nature and art which, though exempt from common accident, are still subject to gradual decay from time, it places in the hands of us all microscopically exact antitypes of objects which, from change or distance, are otherwise inaccessible. To the artist they afford the means of facilitating the otherwise laborious, and often mechanical, task of drawing in detail from nature and from the human figure. "To the physician, to the naturalist, and to the man of science, the uses of photography are various and important, and already the discoveries which have been directly due to this modern art are of stupendous utility. "To the metaphysician, its uses may be sufficiently gleaned from the applications considered in the preceding pages. But to all these classes of men the photographic art derives its chief glory from its application to the stereoscope; and if, for elucidating the principles of vision by means of this application, we have in any degree given a stimulus to the practice and improvement of the photographic processes, our pains have been happily and fruitfully bestowed." _Muller's Processes._--Would you inform me, through the medium of "N. & Q.," what manufacture of paper is best adapted to the two processes of Mr. Muller? I have tried several: with some I find that the combination of their starch with the iodide of iron causes a dark precipitate upon the face of the paper; and with those papers prepared with size, there appears to me great difficulty (in his improved process after the paper is moistened with aceto-nitrate of silver) to procure an equal distribution of the iodide over its surface, as it invariably dries or runs off parts of the paper, or is repelled by spots of size on the paper when dipped in the iodide of iron bath.--A reply to the foregoing question would greatly oblige A CONSTANT READER.