M. C. Lea on the action of Light upon Iodid of Silver. 201 
image. This very remarkable fact, a description of which I 
nape ate early in June last, and which has been since verified 
y other observers,* might seem to be inimical to the physical 
theory. A careful study proved the contrary. Pure iodid o 
silver, still moist, in considerable quantity, freshly precipitated 
and washed, was placed in a porcelain basin and exposed to sun- 
light. It instantly showed the slight darkening above referred 
to, but even after the action of the light and direct sunlight was 
continued for several hours, no reduced silver could be detected. 
In addition to the foregoing, which are direct arguments, is 
to be placed the following indirect. 
, ma- 
ier 
gla ents have been since repeated by Girard with substitution 
lasa and rock erystal, with like results, OR os 
+ 
See paper by Major Russell in Sutton’s Notes, vol. xi, No. 245. 
2 These 4 hav. . 
