“With respect,” says he, “to the means of preparing the binocular photographs, (and in this term I include both Talbotypes and Daguerreotypes,) little requires to be said beyond a few directions as to the proper positions in which it _is necessary_ to place the camera in order to obtain the two required projections. “We will suppose that the binocular pictures are required to be seen in the stereoscope at a distance of eight inches before the eyes, in which case the convergence of the optic axes is about 18°. To obtain the proper projections for this distance, the camera must be placed with its lens accurately directed towards the object successively in two points of the circumference of a circle, of which the object is the centre, and the points at which the camera is so placed must have the angular distance of 18° from each other, exactly that of the optic axes in the stereoscope. The distance of the camera from the object may be taken arbitrarily, for so long as the same angle is employed, whatever that distance may be, _the picture will exhibit in the stereoscope the same relief_, and be seen at the same distance of eight inches, _only_ the magnitude of the picture will appear different. Miniature stereoscopic representations of buildings and full-sized statues are, therefore, obtained merely by taking the two projections of the object from a considerable distance, _but at the same time as if the object were only eight inches distant_, that is, at an angle of 18°.”[50] [50] _Phil. Trans._, 1852, p. 7. Such is Mr. Wheatstone’s rule, for which he has assigned no reason whatever. In describing the binocular camera, in which the lenses must be only 2½ inches distant for portraits, I have shewn that the pictures which it gives are perfect representations of the original, and therefore pictures taken with _lenses_ or cameras at any other distance, must be different from those which are seen by the artist looking at the sitter from his camera. They are, doubtless, both pictures of the sitter, but the picture taken by Mr. Wheatstone’s rule is one which no man ever saw or can see, until he can place his eyes at the distance of _twenty inches_! It is, in short, the picture of a living doll, in which parts are seen which are never seen in society, and parts hid which are always seen.