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Page:Popular Science Monthly Volume 21.djvu/94

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According to this view the odoriferous bodies, or their molecules, have no more to do (in the sense of physical impact) in producing the sensation of smell than a luminous body—a candle or the sun—has to do (by impact) with the sensation of light. There is corporeal impact or touch in neither case. Of course, with each molecule as a center of activity, the effect will be more pronounced at the immediate surface (as with all radiant energies) than at any distance. And, undoubtedly, particles of disintegrating, odorous matter are often brought in contact with the Schneiderian membrane; but the sensation of that impact, if there be any, would be of touch, not of smell, as surely as that, from that point of contact to the sensorium, the effect or influence is conveyed by a vibration—a wave-motion in the "fluid" of the nerve-duct—as the undulations of the luminiferous ether are propagated along the course of the optic nerve to the seat of sensation, where they are translated into light and color. But, if, for any portion of the distance between the internal sense and the fragrant body, the odor, like light, is but a motion, it is safe to assume it for all. The analogy of this mode of odors to that of light and sound is something in its favor.



TO physiologists that part of the function of vision which is concerned in the perception of colors has always been one of great interest, but it was not until the genius of Thomas Young offered them his theory of vision that they had anything like a plausible working hypothesis. This theory, as elaborated and promulgated by Professor Helmholtz, has until very recently been the one most relied upon in explanation of all the phenomena of colored vision. It is, however, a pure hypothesis, since not one of its fundamental principles is a demonstrated or even a demonstrable fact. By a process of deductive reasoning, and most probably with little, if any, experimentation—for it is said that Young prided himself on being independent of the necessity of experiment—the vivid imagination of this original mind seized upon an hypothesis which seemed to satisfy the demands of an acceptable theory, in so far as it accounted for all or nearly all of the observed phenomena. At that time, however, and even when Helmholtz resurrected and revivified the theory, the question of color-blindness had not been investigated to the extent it has within the past ten years, and most physiologists rested content with the belief that at last the true theory of colors had been found,

  1. A paper read before the Philosophical Society of Washington, December 18, 1880.