CHANGES PRODUCED BY THE SOLAR RAYS. 
147 
bined action of these rays — and I have always found the 
result to be a very rapid bleaching of all green vegetable 
powders. The bleaching of the brown and yellow powders 
— jalap, bark, and ginger, is due almost entirely to the blue 
or chemical rays. The chemical examinations which I have 
made of the bleached powders, appear to show that an ab- 
sorption of oxygen takes place under the action of the chemi- 
cal rays — but that the heat rays exert their power princi- 
pally, if not entirely, in removing an atom of combined 
water. 
It will not be difficult to understand how very important 
the changes effected in the constitution of the organic body 
must be, when we consider the very great differences in 
medicinal effects produced in chemical compounds, by the 
addition or subtraction of an atom of oxygen or of water. 
These remarks and results apply with equal force to the 
resins and the fixed oils. The bleaching of the fixed oils 
appears to depend almost exclusively on the action of the 
blue and indigo rays of the spectrum, and although the 
thermic rays produce a little effect upon the resins, it is in 
no respect to be compared to the action of the actinic rays, 
which appear to liberate a portion of oxygen, by which, so- 
larized is rendered much more soluble than unsolarized 
resin. The conversion of linseed oil into a substance re- 
sembling caoutchouc under the influence of the air, is very 
materially modified by the action of the sun's rays, the 
blue rays accelerating the absorption of oxygen, and the 
yellow and red rays retarding it. 
All the changes which have yet been examined upon the 
salts of the metallic oxides, appear to be due entirely to the 
influence of the blue and violet rays, and the alterations in 
colour and character are dependent upon the liberation of 
one atom of the gaseous element from the compound. The 
phenomena connected with these changes are now under 
investigation by the author of this paper, and will shortly 
be published in another form. 
