504 On the Sensitiveness of Silver and other Metccls to Light. 



the so-called " latent photographic image" may be found within these 

 limits. 



JVote, added June 6. — Since the above was written, I have tried the 

 effect of fixing agents, such as hyposulphite of soda and weak solutions 

 of potassium cyanide and ammonia, upon the printed-out images on 

 silvered glass. Neither of them destroys the image, but a very 

 peculiar effect was noticed when a somewhat indistinct printed-out 

 image on silvered glass was treated with potassium cyanide. The un- 

 exposed parts wrinkled up, but not the exposed parts ; after drying, 

 the plate recovered its polished surface, but the exposed parts, instead 

 of appearing light upon a darker ground, appeared darker than the un- 

 exposed parts — the image generally being much clearer and more 

 distinct than it was at first. This effect points to a very strong physical 

 modification of the thin silver film, l)iit requii'es further examination 

 with fresh images upon silver plates. 



