485 BARON VON WREDE ON THE ABSORPTION OF LIGHT 
Ar aay 
— ee 
a/ — 27! cos 9 x 2 + 74 
or 
pit a—ry?d— sa 
a 
where 
Lhd — 27200522 2° + r4 
and 
i eee 
Mi VA —2r cos2r ate 
In the same manner the results of the three retarding causes will be 
Ate Gore Gary da a") 
7 L.M.N. ; 
baa /(1— 29 conte 2 +1) 
2! 
M=4/(i — 27! cos 2x 20 +7) 
N=q/ (1-200 e027 22" + 01), 
From these equations it will be evident that in general A’ or A” 
must attain a partial maximum or a partial minimum as often as one 
U 
of the angles 2 7 2° 20 ; , &c. has completed an entire periphery ; 
where 
that is to say, there must originate in the resulting spectrum as many 
absorptions as would have originated in the sum of each single spec- 
trum. It is therefore easy to account for that which must arise 
from two or more retardations, in the manner which I will now show 
by an example. If we convey light into a vessel into which iodine has 
been brought, and which is then gradually heated so that the iodic 
gas may increase slowly in intensity, the phenomena of absorption 
take place in the manner and order following: as soon as so much 
iodic gas is disengaged that the vessel receives a slightly reddish tint, 
we perceive in the blue light, or rather at the limit between the blue 
and the violet, some slender pale black stripes. The dark stripes be- 
come blacker the more the intensity of the colour increases, and at the 
same time we perceive more dark stripes. With increasing intensity of 
the colour of the iodie gas the light stripes in the blue commence gra- 
dually to decrease in strength, till at last a complete absorption of the 
blue end of the spectrum takes place. In proportion as the entire ab- 
