Mr. Skaife's stereograph.
In the instrument which he has invented for this purpose, and which he calls a Stereograph, he uses lenses only an inch in diameter, the focal length of the combination being also an inch. The lens-tube, ABCD, of the stereograph, as shown of its real size in the annexed figure, in which AB is the front and BC the back, LL a cemented achromatic lens of flint and crown glass, and II an unmounted one, differing only from the ordinary portrait-back combination in being ground—that when the two lenses of which it is composed are together, they touch only at the margin of their inner surfaces. The solar focus of the combined lenses is \( \frac{1}{2} \) inches behind the right-hand surface of the lens II.
Owing to the small size of this instrument, and the small thickness of the glass through which the light passes, the actinic rays are so powerful that the photograph is taken almost instantaneously, and portraits are not deformed by the errors occasioned by the use of large lenses. The small pictures, or stereograms, as Mr. Skaife calls them, when not used for rings, lockets, or bracelets, may be magnified by the enlarging camera without losing any of their sharpness.
The pictures thus obtained are enclosed between two plates of glass, "and when subjected for a definite time to a heat short of that which is required to melt glass, the three substances form but one, as hard and homogeneous as a single piece of crystal." To the picture thus enclosed and preserved from the air, Mr. Skaife gives the name of Chromo-crystal. Some of those which we have seen are extremely beautiful.
A very ingenious improvement upon the binocular camera has been made by Mr. Macraw, of Edinburgh, by which he can take two pairs of stereoscopic pictures upon a prepared plate, which of course must be double the length required for a single pair of pictures. For this purpose the prepared plate is inserted in an inner frame AB, which slips in a groove in the outer rim of the slide MN, with room at CD equal to one of the four spaces, 1, 2, 3, 4, of the plate. When the plate is placed as in the figure, the spaces 2, 4, are opposite the lenses, and receive the picture; and when AB is pushed up to N, the spaces 1, 3, will be opposite the lenses, and receive the second picture.