308 Novel Action of Light. 



NOVEL ACTION OP LIGHT. 



BY NIEPCE DE ST. VICTOR. 



(Translated from " Comptes Ecndus," L T o. 12, 1867). 



I have published, in five preceding memoirs all the experiments 

 which I have made to prove that porous or rough bodies which 

 have been acted upon by light preserve an activity capable of 

 reducing salts of silver in the dark, as though they had been 

 exposed to light. I have shown that this activity is persistent ; 

 that it is preserved for many days in obscurity or in the free 

 air; that if a body had lost this activity, it could be made to 

 resume it on exposing it again to light ; that, supposing a 

 piece of cardboard, was insolated, having been impregnated 

 with nitrate of uranium, or tartaric acid, and shut up in a 

 confined atmosphere, such as a tin case, hermetically sealed, it 

 would have the same activity after several months as it showed 

 •on the first day. 



This activity acts at a certain distance in the dark, for in- 

 stance, and is communicated to a similar body in the same 

 way, but the action does not pass through the glass. 



M. Arnaudon, a chemist of Turin, has repeated some of my 

 experiments in different gases, and the results have been the 

 same as in free air. It would be very important to make an 

 experiment in a luminous vacuum, but I have not as yet 

 been able to do it. I proved the production of this activity 

 upon the edges of a newly-broken china-plate, as well 

 as upon an unpolished sheet of glass, made perfectly clean 

 with distilled water. It could not be said, therefore, in this 

 case, that there was decomposition of the body acted upon by 

 light. I have shown that the effects of light are not owing to 

 phosphorescence, but I have not said whence this activity comes. 

 Many hypotheses have been put forward. Certain persons have 

 denied the fact altogether, which was more simple ; but no one 

 has given a solution to this phenomenon. I said, in my 

 first memoir, that an engraving or a plain sheet of paper hav- 

 ing been insolated and afterwards placed on a layer made sen- 

 sitive to light, such as iodide or chloride of silver, reduces salts 

 of silver in obscurity, as though they had been exposed to 

 light, only much more rapidly. If the sheet is impregnated 

 with nitrate of uranium, or tartaric acid, before being exposed 

 to the light, the reduction of the salts of silver is very quick, 

 especially with the first substance. 



This is, then, my experiment. I placed seven strips 

 of red, orange, yellow, green, blue, indigo and violet glass 



