( 162 ) 
lowering of the temperature. Thus while up to the present we 
observed only the momentary bands Ca Mn £, Sr Mn t -f, Ba Cu we 
have now observed the permanent phase and the lower momentary 
phase, and in Ca Ni 0, Ca Bi y and Ca Bi « 2 , 9rZn a, Ba Bi a^he hitherto 
unobserved lower momentary phase. Thus the prophecy formerly 
made (“1904” p. 483 note 2) concerning these “phosphors” has 
now been found to be fulfilled * *). 
As a general rule one can say about the temperature phases at 
very low temperatures, that the temperature of solid hydrogen (in 
round numbers —260° C.) is low enough to bring all bands of the 
“ phosphors ” of the alkaline earths') into the lower momenta^ phase. 
As the temperature falls from higher values to that of liquid air 
(—180° C.) new bands continually appear in the permanent phase. 
Also at the temperature of liquid air various bands are of long 
duration, the most striking being the persistent and clear afterglow 
of the CaNi-“phosphors” (CaNif? band) (“1904” p. 435). At all lower 
temperatures, however, down to —260° C. one can observe but a 
small continuous afterglow; only the orange-yellow afterglow of the 
BaCu-“phosphors” is here conspicuous for its persistence and clearness, 
having a maximum at —190° C. All other bands either appear in 
the lower momentary phase in so far as they have not already 
gone beyond it, or they pass through a region of permanency lying 
very low and of small intensity (such as BaCu (i at —240 1 C., 
CaMn £ at —250° C.). At the still lower temperature of — 260° C. 
all phosphorescence becomes exclusively momentary*). 
In all the “phosphors” investigated exposure to cold has resulted 
in discovery of only one new band; it is a green band in CaBi 
lying not far from the green heat band CaBi/?, but contrary to this 
it is to be indicated as the lowest cold-band which assumes a state 
of permanency at —255° C, although, as has already been remarked 
in general concerning these temperatures, the intensity is very small. 
*) The permanent yellow-red band of the SrMn-“ phosphors” which had formerly 
remained unnoticed on account of the smallness of the range of the permanent 
phase was now found to be at — 60 3 G. 
*) In the present communication we have left out of account the “phosphors 
of lead, silver, antimony and also of SrCu. 
8 ) A thermoscope that would serve many purposes both at low temperatures 
and at others up to red-heat, could be made out of a number of small pieces o 
different “phosphors” enclosed in a glass tube devoid of air. These should be so 
chosen that the range of permanency of their bands at different points of l e 
desired temperature interval should end as sharply as possible. The temperature 
could then be determined according to whether they glow or not with a de m e 
colour when exposed to lieht. 
