448 
PHYSICS: NICHOLS AND HOWES 
The absorption spectrum of ammonium uranyl chloride, observed 
under the conditions described above, is no less remarkable than the 
spectrum of the fluorescent light. 
It extends from just about 0.5 fx into the ultraviolet and consists, like 
the fluorescence spectrum, of several series of equidistant bands having 
a common frequency interval. 
This interval, expressed arbitrarily in the form lOy^ where jjl is the unit 
of wave length, is approximately 71.0 whereas the interval for the- 
fluorescence is 83.2. 
Our earher observations, without regard to polarization had led to the 
recognition of four series designated as a, y, 8, and three of these 
appeared to consist of doublets. 
c 
f i 
i i ! i 1 i i 
^ 4^ 
1 1 . 1 
li . Mi 
m 
i 
1 1 1 1 M 1 1 
19100 20l00 " ' 
i ^ '1 i I '1 i 
FIG. 4 
The relation between absorption and fluorescence at +20° is briefly 
as follows : 
In the region lying between 0.5075ai and 0.4900/-t which is occupied by 
the fluorescence group of shortest wave length, and which we have termed 
the reversing region, there is an absorption band for each fluorescence 
band and coincident as to position. The reversing region is the most 
unsatisfactory for the study of fluorescence on account of this coinci- 
dence of fluorescence and absorption. It is however possible by the 
use of suitable screens, to almost entirely suppress fluorescence and to 
locate the absorption bands of this region. Towards the red all the 
fluorescent bands form series with a common constant interval of 83.2. 
Towards the violet all the absorption bands belong to similar series 
starting from these reversible bands with a common constant interval 
of 71.0. (See fig. 3.) 
