PHOTOGRAPHY. 



11 



minute the film seems nearly opaque. I take our negative 

 picture, and, at each end of it lay a very thin strip of glass and 

 place the sensitive plate upon them. (The strips of glass 

 are used to prevent the surface of the collodion film being 

 abraded by contact with the other plate.) I expose to the 

 electric light for a second. On removing the plate I can see 

 no trace of an image, but I will endeavour to show you its 

 development. 



Close to the lens (C) of the lantern (B) of the electric light 

 (A) I place a piece of red glass (E) in the clamp (D), for reasons 

 which subsequently will be apparent to you, and immediately 

 in /front of that a glass cell (F) containing a solution of 

 ferrous sulphate slightly acidified with acetic acid. I now 



