Scientific memoirs : being experimental contributions to a knowledge of radiant energy / by John William Draper.

  • John William Draper
Date:
1878
Catalogue details

Licence: Public Domain Mark

Credit: Scientific memoirs : being experimental contributions to a knowledge of radiant energy / by John William Draper. Source: Wellcome Collection.

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    suffice. But how is it possible to restrict the chemical force of the spectrum to the region of the more refrangi- ble rays, in face of the fact that compounds of silver such as the iodide, which have heretofore been mainly relied upon to support that view, and, in fact, originated it, are now proved to be affected by every ray from the invisible ultra-red to the invisible ultra-violet; how, when it is proved that the decomposition of carbonic acid, by far the most general and most important of the chemical actions of light, is brought about not by the more refrangible, but by the yellow rays ? The delicate colors of flowers, which vary indefinitely in their tints, originate under the influence of rays of many different refrangibilities, and are bleached or destroyed by spec- trum colors complementar}?- to their own, and, therefore, varying indefinitely in their refrangibility. Towards the indigo ray the stems of plants incline; from the red their roots turn away. There is not a wave of light that does not leave its impress on bitumens and resins, some undulations promoting their oxidation, some their deoxidation. These actions are not limited to decompo- sition ; they extend to combinations. Every ray in the spectrum brings on the union of chlorine and hydrogen. The conclusion to which these facts point is, then, that it is erroneous to resti'ict the chemical force of the spectrum to the more refrangible, or, indeed, to any s,])ecial region. There is not a ray, visible or invisible, that cannot produce a special chemical effect. The dia- gram so generally used to illustrate the calorific, lumi- nous, and chemical parts of the spectrum serves only to mislead. While thus we find that chemical action may take place throughout the entire length of the spectrum, the remarks that have been made in a previous Memoir (XXVI.) respecting the differences of calorific distribu-