Note on the stereophotochromoscope : a new optical instrument / by David Fraser Harris.

  • Fraser-Harris, David Fraser, 1867-1937.
Date:
[1895]
Catalogue details

Licence: Public Domain Mark

Credit: Note on the stereophotochromoscope : a new optical instrument / by David Fraser Harris. Source: Wellcome Collection.

Provider: This material has been provided by The University of Glasgow Library. The original may be consulted at The University of Glasgow Library.

    4/10 (page 122)
    12^ MR DAVID FRASER HARRIS. reflected is now provided to illuminate it: if it originally reflected only one kind of coloured ray—a primary—it can And that light again to tint it; if it reflected two or three kinds of rays, they are all there again for simultaneous treatment by it. The crucial test is in the case of colours not present as such in the spectrum, e.g., the 2mrple of plums or grapes: the photo- graphs of these objects are combined into one image, as of solid plums or grapes, now lit simultaneously by both red and violet light—a fusion which produces the sensation of purple ; and so on for all other shades and tints of coloui\ To quote Ives' words—The three images of the chromogram represent the action of all incident light upon the respective fundamental colour-sensations, and the light by which each image is illumi- nated m the lantern or heliochromoscope represents the sensa- tion itself. This is the gist of the whole matter: the heho- chromoscope is the older name for the stereophotochromoscope, and by it a single image may be thrown on a screen instead of the double one into the eyes. Of course, when so projected on to a flat surface and viewed with the naked eye, as in a lantern demonstration to a large number of people, the illusion of soHdity in the coloured picture is entirely lost, that being an effect due to optical contrivances produced by its very nature only in the brain of each individual looking into the instrument. While using the projection-lantern, the whitest of light—that of the electric arc if possible—must be employed, when the results are very satisfactory. To those conversant with the practical details of photography, a criticism will at once suggest itself:—How can the three chromograms be taken simultaneously on the one plate, seeing that the time of exposure for red light is much longer than for any other colour? This is a difficulty which the inventor overcomes in two ways: he either reduces the intensity of the other two more active colours by interposing ground or smoked glass in the path of their rays, or he employs a larger diaphragm for the red light than for the green or violet. What strikes one on looking into the stereophotochromoscope is the brilliance or vividness of the colours of the object—an appearance partly due to the image being seen against a dark background, and partly to its being reduced, or less than life -