and on the chemical action of the Solar Spectrum. 269 



beneath the iodhie the paper became richly iridescent. The 

 colours changed to a uniform violet tint upon a few minutes' 

 exposure to direct sunshine. 



7. Papers already darkened by sunlight during prolonged 

 exposure to the influence of the dissevered rays of the spec- 

 trum, assume a variety of colours. The same changes may 

 be eifected by carefully arranging glasses, and placing the 

 photographic preparations beneath them. I shall copy ex- 

 actly the memoranda of my journal. 



Dec. 12, 1839. — I placed under blue, green, yellow, and 

 red glass the following papers : 



A. Muriate of a7nmo?iia, with two washings of solution of 

 the nitrate of silver, darkened by exposure to a rich chocolate. 



B. Muriate of 7na7iganese. Silver, two washings, dark- 

 ened to a full brown. 



C. Iodide of potassimn. Silver, one washing, darkened 

 to a yellow brown. 



D. Iodide of potassitim and silver, two washings, dark- 

 ened to a red brown. 



E. Chloriodic acid. Silver two washings, darkened to a 

 rich bronze. 



F. Chloriodic acid with Liquor potasses. Silver, two wash- 

 ings, darkened to a blue-brown. 



Dec. 13. — After twelve hours exposure to the dull light of 

 rainy weather, the paper E has become blue under the blue 

 glass. No change is apparent on the others. 



Dec. 27. 



Colours of Glass. 



Yellow. 



Red. 



Dirty yellow. 



Red. 



Blue brown. 



Red. 



No change. 



Red brown. 



Rich brown. 



Brick red. 



Darkened. 



Dusky red. 



Bluish. 



Reddened. 



Blue. Green. 



A. has become Olive. I Deep green. 



B Deep brown. Bat colour. 



C Do. Darkened. 



D Black. Light brown. 



E Blue black. Darkened. 



F Blackbrown. Dull plum. 



Jan. 2, 184-0. — All the papers go on increasing the distinct- 

 ness of their colours, except E and F, which have assumed 

 different shades of blackness. 



(E a7id F iioere removed, and a paper G, prepared mth 

 muriate of baryta and two washifigs of silver, darkened to a 

 chocolate, substituted.) 



Feb. 7. Colours of Glass. 



Red. 

 Purple. 

 Red. 

 Brown. 

 Red brown. 

 Reddish. 





Blue. 



Green. 



Yellow. 



A 



Rich olive. 



Green. 



Yellow. 



B 



Black, 



Chocolate. 



Light brown. 



C 



Do. 



Red brown. 



Do. 



D 



Chocolate. 



Umber brown. 



Black. 



G 



Bright olive. 



Yellow brown. 



Pale olive. 



