276 M. C. Lea—Aetion of the less refrangible rays of Light 
experiments were made on the two used together. They were 
used in equivalent proportions and in such quantity that the 
paper containing the two salts together should take up exactly 
as much silver as the papers prepared with AgBr and AgI sep- 
arately. The result demonstrated a materially greater sensitive- 
ness to both red and green light than with either used sepa- 
rately. The experiment was not extended to the yellow, but 
it would doubtless have given similar results, as also the more 
refrangible rays of the spectrum. 
t may be worth mentioning, in passing, that the result of 
this part of the investigation led to the making of a series of 
experiments on the introduction of silver iodide into the 
“emulsion process” for preparing photographic dry plates. 
The result was that when either equal or equivalent quantities 
of AgBr and AgI were employed, nothing material was gained, 
Agland AgBr. There was found a moderate superiority of sen- 
sitiveness in AgI, though much less marked than in the case of 
the red and green rays. Exposure under a negative for three 
seconds to a weak diffused light sufficed to produce a strong 
latent image on both the AgI and AgBr papers, but most strong 
upon AglI. 
As respects silver iodide, my opinions have always differed 
from those which have prevailed among photo - chemists. 
Many years ago I proved the opinion that silver iodide, abso- 
lutely isolated, was insensitive to light, to be erroneous. 1! cov- 
ered glass plates (preferably ground glass, for better adhesion) 
with thin specular films of silver, and then iodized these throug 
and through by means of a solution of iodine, and succeeded 
