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584 History of Three-Color Photography
latter in which each picture is formed complete in colors on the screen. The subject has, therefore, been divided into these classes for treatment.
The Additive Method With Persistence of Vision. — The first suggestion for this process may justly be ascribed to Chas. Cros,1 (p. 611) for he said : "Le phenakistoscope, remis en vogue dernierement sous le nom zoetrope, me dispense de longues explications sur le svnthese successive. Les images elementaires sont substitutes rapidement les unes aux autres sous les regards et les impressions produites sur la retine se confondent. On obtient ainsi la combinasion des trois couleurs pour tous les points de l'image resultante. Ce procede s'applique aux projections sur eeran, aux positifs transparents, et aux positives a vue directe. Les instruments sont plus simples que le phenakistoscope, car il n'y a que trois figures elementaires, au lieu de vingt ou trente. De pareils instruments sont tres-faciles a imaginer et realiser. J'en donnerai les dispositifs si on me les demande. II est a peine besoin de dire que le principe de cette synthese successive est experimentalement demontre par le disque tournant a secteurs colores."
Anglicized : the phenakistoscope, revived lately under the name of the zoetrope, excuses me from long explanations on successive synthesis. The elementary images are rapidly substituted the one for the other in the eyes and the impressions produced on the retina recombine. This method is applicable for projection on a screen from transparent positives or from positives viewed direct. The instruments are more simple than the phenakistoscope, for there are only three elementary images, instead of twenty or thirty. Similar instruments are very easy to imagine and to realize. I will give the arrangements if anyone wants them. It is scarcely necessary to say that the principle of this successive synthesis is experimentally proved by the revolving disk of colored sectors.
Although Cros had not in mind in all probability motion pictures, yet the principle of persistence of vision in colors is clearly stated. This method has practically fallen into disuse, therefore, the notes thereon have been curtailed as far as possible.
The first patent that has been found was granted to H. Isensee2 and he placed in front of the lens, both in taking and projection, a rotary shutter with three 120 degrees sectors in the usual colors. W. FrieseGreene3 appears to have had some confused notion of a similar process, for he proposed to use a lens composed of three colored sectors, or a rotary color shutter or a ribbon shutter. The images were received on one plate, and it was claimed that a transparency from the negative thus obtained, showed colors when projected in the same way. The supposed results were, of course, an optical impossibility ; but the patent is interesting because of the suggested shutters. B. S. Philbrook4 had a somewhat similar idea, adopting, however, Cros' idea of the zoetrope. W. N. L. Davidson5 would use a shutter with opaque sectors between the color