Novel Action of Light. 309 



•upon a sheet of paper. After insolation, I have applied this 

 sheet of paper to another sheet covered with iodide or chloride 

 of silver, and have then left them in contact, in the dark, for 

 twelve hours. I then saw that the bands of red, orange, 

 yellow and green glass, had not made anjr impression on the 

 sensitive paper, while the blue, indigo, and violet bands had 

 darkened it. I repeated this experiment upon paper or card- 

 board impregnated with nitrate of uranium, or tartaric acid ; 

 the sensitive layer was much more coloured in the parts cor- 

 responding to the same rays than I have indicated above. 

 When the sheet of paper containing nitrate of uranium, or 

 tartaric acid, has been insolated, this activity can be easily 

 proved by pouring a solution of nitrate of silver, in form of a 

 train, upon the insolated part. A very strong colouring is 

 immediately seen in the blue, indigo, and violet rays, and not 

 any in the four first, except the exposition to light has been 

 very much prolonged. In this case a slight colouring is seen 

 in the green, yellow, and red rays, but not any in the orange. 

 If bands of glass are placed on a sheet of gummed paper, and 

 it is exposed for about an hour to solar light, on pouring a 

 solution of iodide of potassium on the part covered with the 

 seven bands of glass, the parts of the paper corresponding to 

 the violet, indigo, and blue rays, would be observed to take a 

 brick-red tint, while the green, yellow, orange, and red rays 

 would remain unchanged. 



If an iodide of silver is formed by pouring on nitrate of silver 

 before the iodide of potassium, in the dark, the iodide of silver 

 would be coloured in the most refrangible rays. By this means 

 a sheet of paper can be insolated under a press, and a positive 

 proof obtained in the dark, which can be strengthened by 

 means of sulphate of iron. I ought also to mention, that I 

 have made experiments with coloured glasses upon white and 

 coloured stuffs, and the stuffs and the colours were only altered 

 by the light under the violet, indigo, and blue glasses. I 

 should say that light has less action under a violet than a white 

 glass, and less under the latter than in open daylight. 



Conclusions. — After these experiments, it can be said that 

 light has only a destructive action in the most refrangible rays. 

 That is known, it will be said ; but this persistent activity 

 was not known before my experiments, and now I demon- 

 strate that it is owing to chemical rays, and that it has the 

 same effect as direct light in reducing salts of silver. 



