The Optical Magic Lantern Journal (May 1901)

The Optics of Trichromatic Photography.—Part VI. THe Trari~t Taytor MemoriaL LECTURE. : Continued from page 48. In March, 1894,* C, Nachet, of Paris, patented a device in which two of the images were blended to the right eye by the aid of a thinly silvered or platinised mirror, and |! the third image, made from a different view point, was | seen directly with the other eye. This was an attempt to make a combined photo-chromoscope and stereoscope ; but, owing partly to the fact that very few people (if any) can successfully “blend” two primaries through two eyes, it was soon abandoned. This idea, first published by M. Nachet, is fully set forth in the mémoire attributed to Louis Ducos du Hauron as of the date July 14, 1862, but first published in 1897; nevertheless, it is credited to Nachet on page 360 of the same book in which it first appears as belonging to Jiouis Ducos du Hauron in 1862. | in September, 1894, Carl Zink, of Gotha, published a description of a photo-chromoscopé having three rectangulur ‘‘steps,’’ and two transparent and one ordinary silvered mirror, and a “cosmorama"' lens. The new features in this device were the horizontal disposition of the ateps, inclination of the mirrors in the horizontal plane, and all disposed to reflect from their | upper surfaces, and an adjustment of angle to secure the . best direct illumination of the reflected images. A ' horizontal disposition of the three mirrors had never : before been published, although it appears in the Du Hauron 1862 mémoire already referred to, with one of them disposed to take the reflection from the under side. Zink’s publication was anticipated by my application for a patent upon the same and several other important improvements in the ‘step’ photo-chromoscope with transparent mirrors. My patent application, dating July 3rd, 1894,¢ discloses not only the arrangement shown by Zink, but (1) an efficient contraction to two steps instead of three, whereby the apparent area of the picture is nearly doubled, (2) the use of coloured glass reflectors by which doubling of outlines is avoided without the use of convex lenses or ‘thin silvering,”'t and the construction and adjustment proportionately simplified, (2) a stereoscopic construction, whereby the | illusion of reality is brought to perfection, (4) a modification by which the images are disposed in line upon a single plate. None of theese ideas had been published before my dates of record. Some months after the publication of my patent, Nachet claimed thc same construction on the strength of a clause in his patent which was to the effect that two transpsrent mirrors instead of one could be used in his three-image sterao-chromoscope. . The natural inference from the wording of this clause was that he meant one in front of each eye, the construction tince adopted in the “ Kromaz,”’ and not an arrangement involving a totally different idea like my own. Even ifit is assumed * French Patent No. 237,394, March 29, 1894. + U.S, Patent No. 531,040, published December 18th, 1894. _ 2 The possibility of ermploving colonred glass reflectors was first disclosed in my U.S. Patent No. 475,084, published May 17th, 1892; but the particular relation of the colours of the glasses to the respective images was first published in the Journal of the Society of Art«, May 19th, 1893, p. 666, and patented in the U.S. in 1894. In_ his treatise published in 1897, Alcide Duecos Du Hauron publishes this for the first time as a proposition of his own; and it is only one of many ideas which have been claimed by Du Hauron only after they had been published or patented by others. Even Olerk-Maxwell and Harry Collen are totally ignored in this book. o7 that he may have meant that two trausparent mirrors could be used in front of one or both eyes, the fact that he so disposed his transparent mirror as to reflect from below proves conclusively that he had then no thought of direct lighting of the reflected images and the use of a folding chromogram, which I patented and which he reproduced, along with other details shown in my patent drawings, such as a tray base and strut for fixing the inclination, months after the publication of the patent. Inclination of the mirrors in a horizontal plane, with the reflections taken from the upper surfaces, and the three images disposed in line upon one plate, patented and first published by me, also appears in Du Hauron’s melano-chromoscope. As before stated, inclination of the mirrors in a horizontal plane, but at opposite angles, is djsclosed in the Du Hauron 1862 mémoire: It is remarkable. that the three-image stereoscopic construction patented by Nachet in 1894, a stereoscopic construction with tliree pairs of images, a two-step construction, methods of stereoscopic projection, and other ideas first made public by others, appear in this mémoire, and are first published as Louis Ducos Du Hauron’s inventions twenty-eight years after he was challenged by Charles Cros to show a record antedating Cros’s sealed mémoire of 1867. Du Hauron’s reply to this challenge appeared in Cosmos, July 24, 1869, when he said, ‘'I myself could have, at the conception of my idea {which he then dates back ‘ five or six’ years] consigned its generalities to a sealed letter... . I gave up to the higher ambition to give to society and to France a system of heliochromy sufficiently elaborated,’ etc. . This is his reply in 1869, seven years after it is now stated that he had prepared expressly for presentation to the Institute of France a meémoire of nearly 3000 words, describing a remarkably elaborate system, and that this mémoire was duly acknowledged and commented upon by M. Lélut, and read by at least one other member of the Institute, preserved oll this time, and even now referred to as a ‘‘ publication” in 1862. Although it may be inferred that his failure to get his mémoire presented to the Institute decided him to try to reduce the method to successful practice before trying again, it would seem most natural that he should have produced such conclusive proof of priority in reply to Cros if he was able to ; do so. It is quite probable that the inconsistencies which I have noted may be satisfactorily explained away, but it seems proper, under all the circumstances, to raise the question, and I hasten to say that, for reasons well known to many, this can be done without questioning the integrity of Louis Ducos Du Hauron. I don’t think the question would have been raised in my own mind if I had not already regularly found my own published ideas reappearing in France as French inventions, dated back without evidence, and my own publications totally ignored. My 1894 ‘two-step '’ photo-chromoscope (to which I have given the distinctive name Kromskop) has never: been rivalled by any other form of viewing device, and has been finally perfected by two ‘improvement ’’ inventions. As originally constructed, it was found that the inclination of the transparent reflectors between the eye and the green image introduced such a distortion of that image that the red and blue images, reflected from plane surfaces, could not be perfectly superposed upon it. The reason for this can be readily shown by tracing the path of the rays from the top and bottom of the green picture to the eye, both direct and as changed by refraction through the inclined transparent mirrors, the amount of distortion depending upon the thickness of the glasses;