78 Scientific Proceedings, Royal Dublin Society. 



a fogging of the plate did not affect this portion of the plate to the same 

 extent as the remainder. 



Some facts observed. — When the anode is placed near enough to the 

 kathode to allow the region affected by the anode to reach that round the 

 kathode, it is observed that at the junction of the two regions the blackening 

 of the plate is sometimes more marked, but the anode effect seems to be 

 arrested and to travel no further (Plate II., fig. 10). 



Conclusio)!. — The results of these experiments suggest the possibility of 

 their being connected with the reactions studied by Lodge, Whethem, 

 and others in gelatinous and other solutions, and the results obtained are no 

 doubt due to some action of metallic ions on the sensitive salts contained in 

 the coating of the photographic plates. 



Wliile many suggestions might be made as to the nature of the reactions 

 involved in these phenomena, I do not propose to discuss the action of the 

 various substances employed in giving rise to a blackening of the plate. The 

 question is one involving very obscure and little known reactions, and in the 

 present state of our knowledge it is sufficient to put on record these results 

 as a contribution to the accumulation of facts which have been ascertained 

 concerning the blackening of photographic plates. 



