Page:Popular Science Monthly Volume 45.djvu/557

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IT is difficult to give a simple explanation of color. Physicists declare that it is the result of a vibratory movement; and metaphysicians who listen to them pretend to comprehend this. Although it is not clear, this definition is nevertheless the only one it is possible to give. There exists a vibratory movement which is translated into heat, light, and electricity. There are possibly also movements that determine the various psychological phenomena—other vibrations no less confused, no less vague, no less mysterious to our minds than the physical vibrations.

Many persons will be surprised when they are told that M. Lippmann, the discoverer of photography in colors, was never engaged in photography. He discovered in the play of luminous vibrations what he was trying to define in the theory of sonorous vibrations. Being charged with the exposition in his lectures at the Sorbonne of the principles of acoustic phenomena, he sought especially to demonstrate to his students that the pitch of the sound given out by an organ pipe depended on its length and not upon the particular metal of which it was constructed. He was at once struck with the results that might be drawn from this phenomenon; he asked if it would not be possible to transport into the domain of light the curious property that seemed to be involved in that of sonorous vibrations. This conception, in its elegant simplicity, might be said to be a conception of genius. There was nothing in it like the attempts that were made earlier in the century to fix colors photographically. The first experiment in this direction was made in 1810 by Prof. Seebeck, at Jena. He tried to impress the colors of the solar spectrum on a paper covered with a film of chloride of silver. His experiments, though not successful, were much talked about. They were taken up again in earnest in 1841 by Sir John Herschel. Failing with chloride-of-silver paper, he tried bromide and iodide of silver, and natural products, such as guaiacum root. He succeeded by some of these processes in temporarily fixing a few colors on sensitive papers. Such results were encouraging. We were then at the beginning of photography. But these successes were soon surpassed by the experiments of Edmond Becquerel, who succeeded, in 1848, in obtaining upon a silver plate covered with a film of violet subchloride of silver the impression of all the colors of the solar spectrum. Unfortunately, the colors stored up in this manner vanished as soon as the plate was exposed to the light. All attempts to preserve them by means of a fixing bath failed. At every effort the color disappeared. The impression of the spectrum colors by the