Chemical Force in the Spectrum. 31 
examine the details of this phenomenon in the spectrum. His 
memoir is in the Philosophical Magazine (Jan., 1844). When 
seeds are made to germinate and grow for a few days in dark- 
ness, they develop vertical stems, very slender and some 
inches in length. These, on being placed so as to receive the 
spectrum, soon exhibit a bending motion. The stems in other 
parts of the spectrum turn toward the indigo; those in the 
indigo bend to the approaching ray. Removed into darkness, 
they recover their upright position. These movements are the 
most striking of all actinic phenomena. I have often witnessed 
them with admiration. 
“ The first action of light is perceived in the mean red rays, 
and it attains a maximum incomparably greater at that point 
than elsewhere. The next part affected is in the indigo, and 
accompanying it there is an action from + 10% to + 36°0 of 
the same scale (Herschel’s) beginning abruptly in Fraunhofer’s 
ue. So striking is this whole result, that some of my earlier 
spectra contained a perfectly neutral space, from—50 to +20.5, 
in which the chlorophyl was in no way changed, whilst the 
solar picture in the red was sharp and of a dazzling white. The 
maximum in the indigo was also bleached, producing a linear 
Spectrum, as follows: 
Tn which the orange, yellow and green rays are neutral. These 
it will be reenshored are active in forming chlorophyl. Upon 
longer exposure the subordinate action along the yellow, etc., 
Securs, but not until the other portions are perfectly bleached. 
“In Sir J. Herschel’s experiments there remained a salm 
color after the discharge of the green. This is not seen when 
ch orophyl is used, and is due to a coloring matter in the leaf, 
soluble in water, but insoluble in ether.” 
T have quoted these results in detail because they illustrate 
a striking manner the law that vegetable colurs are destroyed 
by rays com lementary to those that have produced them, and 
ree proof that rays of every refrangibility may be chemically 
Ctive, 
in 
At this poirt I abstain from adding other instances showing 
that chemical changes are brought about in every part of the 
Spectrum. The list of cases here presented might be indef- 
