( 164 ) 
within whose limits this occurs is the region of permanency of the 
band investigated. In this manner various experimental results given 
in this communication were obtained. 
Thus the region of afterglow of the band BaCu «, extends from 
— 260° C. to -}- 350° C. *), and is therefore unusually extensive; the 
region of warming-glow of this band is equally wide. An example 
of a narrow range on the other hand is given for the yellow band 
CaNi £ from —j80°C. to — 100° C., and in this case the warming- 
glow is restricted to within the same narrow limits. 
The storing of the effects of illumination is at the temperature of 
solid hydrogen particularly large and unusually complete. If, after 
illumination of the phosphorescent substance atj— 260° C. it is slowly 
warmed, it remains nevertheless quite or nearly quit© dark; but 
when the lower limit of the permanent phase is passed, the emission 
of light begins almost at once with great intensity. It is just the 
non-appearance of the effects of the illumination in the lower momentary 
phase that makes it comprehensible that the storing should reach 
such a great value. Its value remains, however, beneath a certain 
limit. If the illumination in liquid hydrogen is continued longer and 
longer, the intensity of the warming-glow finally ceases to increase. 
This must be explained by the circumstance that as soon as the 
centra which occasion the bands have obtained their full charge they 
adopt other periods of oscillation (corresponding With the periods of 
the light which can extinguish the phosphorescence*)) and could not 
thus in any case absorb any more of the exciting light. 
With regard to the intensity of the light during the illumination 
in the lower momentary phase, we found that for a definite exciting 
wave-length, e.g. the light passed through our ultra-violet filter, the 
various bands behaved in widely differing manners. Bands that at 
260° C. are of very small intensity in the lower momentary phase 
are e. g. Ca Mn «, Sr Mn a , while others such as Ba Cu Ba Bi a t , 
radiate with great clearness under the same circumstances. The latter, 
however, also lose their light quickly after illumination — a behaviour 
corresponding with the known properties of the lower momentary 
phase — and show also the very perfect storing which we have just 
mentioned. Later ($ 7 of this Communication) we shall bring these 
different behaviours of the various bands under one general point o 
view, by making the fundamental assumption that the quantitative 
relation between the momentary process and the simultaneous continuous 
l ) At temperatures above the ordinary, the intensity of both the responsive glow 
and the afterglow with ultra-red excitation is indeed very small. 
*> “1909”. Also P. Lenard and Sem Saelano Ann. d. Phys. 28 p. 499, 1 
