and on the chemical action of the Solar Spectnm, 269 
beneath the iodine 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 effected 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 ammonia^ with two washings of solution of 
the nitrate of silver, darkened by exposure to a rich chocolate. 
B. Muriate of manganese. Silver, two washings, dark- 
ened to a full brown. 
C. Iodide of potassmm. Silver, one washing, darkened 
to a yellow brown. 
D. Iodide of potassium 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 potassce. 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, 
A. 
B. 
C. 
D. 
E. 
F. 
has become 
Blue. 
Olive. 
Deep brown. 
Do. 
Black. 
Blue black. 
Black brown. 
Green. 
Deep green. 
Bat colour. 
Darkened. 
Light brown. 
Darkened. 
Dull plum. 
Yellow. 
Dirty yellow. 
Blue brown. 
No change. 
Rich brown. 
Darkened. 
Bluish. 
Red. 
Red. 
Red. 
Red brown. 
Brick red. 
Dusky red. 
Reddened. 
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 and F >were removed^ and a paper G, prepared nsoith 
muriate of baryta and two washings of silver darkened to a 
chocolate substituted,) 
Feb. 7. Colours of Glass, 
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. 
Red. 
Purple. 
Red. 
Brown. 
Red brown. 
Reddish. 
