At the meeting of the British Association in 1853, M. Claudet endeavoured to establish some rules for the angle at which photographic pictures must be taken, in order to produce the best effect of relief and distance without exaggeration. He observed, that in looking at a single picture with two eyes, there is less relief and less distance than when looking at it with one eye, because in the latter case we have the same effect we are accustomed to feel when we look at the natural objects with one eye; while, if we look at the single picture with two eyes, we have on the two retinæ the same image with the same perspective, which is not natural, and the eyes have not to make the usual effort for altering their convergence according to the plane on which the object observed is situated. This inaction of the convergence of the eyes diminishes the illusion of the picture, because the same convergence for all the objects represented gives an idea that they are all placed on the same plane. The photographic image being the representation of two different perspectives, we must, when we look at them in the Stereoscope, as when looking at the natural objects themselves, converge, more or less, the axes of the eyes. Therefore we make the same effort, and have the same sensation in regarding the combined photographic pictures, as when we look at the objects represented. Sir David Brewster has suggested various applications of the Stereoscope; viz., to painting, to sculpture and engineering, to natural history, to education, and to purposes of amusement. The latter is the principal purpose to which the instrument is at present applied; and some of the many ways in which it may contribute to delight the spectator are pointed out in Sir David Brewster's book.