32 J. W. Draper—Distribution of 
initely extended, if these did not suffice. But how is it pos- 
sible to restrict the chemical force of the spectrum to the region 
of the more refrangible rays, in face of the facts 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 refrangi- 
bilities, and are bleached or destroyed by spectrum colors com- 
plementary to their own, and, therefore, varying indefinitely in 
their refrangibility. Toward the indigo ray the stems of plants 
incline; from the red their roots turn away. There is nota 
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 decompositions ; 
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 restrict the chemical force of the spectrum to the 
more refrangible, or, indeed, to any special region. There is 
not a ray, visible or invisible, that cannot produce a special 
chemical effect. e diagram so generally used to illustrate 
the calorific, luminous, 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 
ave been made in the previous memoir (this Journal, Sept., 
1872), respecting the ditsrasths of calorific distribution in 
844. ey are referred to in the Philosophical Magazine 
(June, 1845). As they were obtained on silver plates made 
The fixed lines were beautifully represented in the photo- 
graphs. They were, however, so numerous and so delicate, 
