This instrument differs from the preceding in having a single reflector, MN, M′N′, for each eye, as shewn in [Fig. 31], and the effect of this is to exhibit, at the same time, the raised and the hollow cone. The image of B, seen by reflexion from MN at the point C, is combined with the picture of A, seen directly by the right eye R, and forms a hollow cone; while the image of A, seen by reflexion from M′N′ at the point C′, is combined with the picture of B, seen directly by the left eye L, and forms a raised cone.
Fig. 31.
Fig. 32.
Another form of the double reflecting stereoscope is shewn in [Fig. 32], which differs from that shewn in [Fig. 31] in the position of the two reflectors and of the figures to be united. The reflecting faces of the mirrors are turned outwards, their distance being less than the distance between the eyes, and the effect of this is to exhibit at the same time the raised and the hollow cone, the hollow cone being now on the right-hand side.
If in place of two right or two left eye pictures, as shewn in Figs. [29], [31], and [32], we use one right eye and one left eye picture, and combine the reflected image of the one with the reflected image of the other, we shall have a raised cone with the stereoscope, shewn in [Fig. 31], and a hollow cone with the one in [Fig. 32].
The double reflecting stereoscope, in both its forms, is a general instrument for portraits and landscapes, and thus possesses properties peculiar to itself.
The reflectors may be glass or metallic specula, or total reflexion prisms.