ECLIPSE SYSTEM OF STEREOSCOPIC PROJECTION.
To the same inventor is due the con ception, in 1558, of the Eclipse System of Stereoscopic Projection, which is carried out in the following manner. The two elements forming the stereoscopic pair are made into positive transparencies and placed respectively in the two lanterns A B (Fig. S49). The direction of the objectives is so arranged that their axes meet in the centre of a common screen The eclipse system described in the last paragraph has disadvantages of a serious nature. As Fig. 850 shows, it is necessary that the shutter used by each spectator should work synchronously with the one revolving in front of the lanterns, a con dition not easily complied with when a large audience is involved. For this reason the system has fallen into disuse. But stereoscopic effects are so highly ap preciated, that inventors have constantly devised fresh means, and side-by-side a D, so that the position of both pictures is the same. A shutter G revolving on an axis at E uncovers the objectives of the lanterns alternately. A similar shutter It is arranged to revolve before the observer's eyes at L and R, both shutters being made to turn synchronously, the result being that the left eye L sees only the left element of the stereogram pro jected upon the screen, and the right eye II sees only the right element. Hence
the two, although not seen at the same moment of time, succeed each other so rapidly that continuity of impression is preserved, which, of course, produces a stereoscopic effect. The manner in which the simultaneous action of the shutters is accomplished will be seen by reference to Fig. S50. It is obvious that the eclipse system is applicable to the upright bi unial lanterns of more recent design.
projection next made its appearance. A typical example of this system is shown by Fig. 851. The dissimilar pictures are projected side by side upon a screen A B, and viewed by the two eyes at L R. In front of the right eye a a reflect-prism E is placed. The rays coming from B are bent in their course, so that the imago of n is seen, not at the point it actually occupies, but superimposed upon A, which is viewed direct with the other eye L. The result is, consequently, a stereoscopic effect. The side-by-side projection system is capable of much variation as regards the viewing devices. Thus, if the prism was exchanged for a pair of plane mirrors facing each other, but not quite parallel, the same result would follow. Other variations might be made in which more than one prism or two mirrors arc used, but the example given will suffice.