Page:Popular Science Monthly Volume 8.djvu/487

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471
THE NATURE OF FLUORESCENCE.

save by a process of evolution upward? How could their numerous relations with each other, and their regular serial arrangements into groups, be better explained? In this, as in other problems, the hypothesis of evolution is the simplest, most natural, and best in accordance with facts. Toward it all the lines of argument presented in this article converge. Atomic weights, specific volumes, and spectra, all unite in telling the same story, that our many elements have been derived from simpler stock.

I know that all this is only speculation, but surely it is not baseless. Science is constantly reaching forward from the known to the unknown, partly by careful experiment, and partly by the prophetic vision of thought. It first discovers facts, and then seeks to interpret them, although oftentimes the interpretation is not capable of absolute proof. So with the material of this article. We have seen that many relations connect in some mysterious way those bodies which we commonly regard as simple, and we have sought to determine their meaning. What can they mean, save that the elements are not elementary? How could the elements have originated but by a process of evolution?

 

THE NATURE OF FLUORESCENCE[1]
By Dr. EUGENE LOMMEL,

PROFESSOR OF PHYSICS IN THE UNIVERSITY OF ERLANGEN.

THE question now arises. What becomes of the rays that have undergone absorption? Are they in fact, as they appear to be, annihilated? A series of phenomena now to be considered will give us an answer to these questions.

If water containing a little esculine, a substance contained in the bark of the horse-chestnut in solution, be placed in a flask, and the PSM V08 D487 Illustration of fluorescence.jpgFig. 1.—Illumination of Flourescence. rays of the sun or of the electric lamp, concentrated by a lens situated at about its focal distance from the vesel (Fig. 1), be directed upon it, the cone of light thrown by the lens into the interior of the fluid will be seen to shine with a lovely sky-blue tint. The particles of the solution of esculine in the path of the beam become spontaneously luminous, and emit a soft blue light in all directions. The cone of light appears brightest at the point where it enters into the fluid through the glass, and quickly diminishes in brilliancy as it penetrates more deeply.

There are great numbers of fluid and solid bodies which become

  1. From "The Nature of Light," No. XIX. of the "International Scientific Series."