M. C. Lea—Influence of Color upon Reduction by Light. 205 
tion of silver through the agency of gallic acid or other reduc- 
ing agent, thus producing a true “development.” It is with 
these images developed by gallic acid that we shall have to do 
in this and the following section. 
Silver iodide papers, imbued with various coloring matters 
and containing free silver nitrate, were exposed to the different 
rays with the following results: 
and mauveine increased the sensitiveness to the blue rays a 
little, coralline was without effect, aurine and rosaniline dimin- 
ess. 
Violet rays. Aniline blue, green and mauveine all consid- 
erably increased the sensitiveness, coralline increased it a little, 
aurine and rosaniline diminished it a little. ith ordinary 
white light the order of sensitiveness was the same as in the 
Violet rays, 
_ It does not appear that there exists any general law connect- 
ing the color of the substance placed in contact with the silver 
lodide, with increased or diminished sensitiveness to particular 
ra 
Silver Bromide. 
_ Silver bromide is at once the most eae of all the sensi- 
ifficult as to the exact 
made ; thirty-five complete spectra were obtained, besides prints 
from detached portions of the spectrum. e 
substances in the order of the greatest sensibility which they 
conferred, beginning with those that gave the greatest. 
