( 1«5 ) 
process in one and the same band differs according to the wave¬ 
length which gives rise to the processes. 
§ 5. Response to illumination by long waves {red and ultra-red) 
and subsequent extinction. It has already been shown (“1909”, p. 7 l 2 )) 
that the action of ultra-red upon the “phosphors” consists of a local 
molecular rise in temperature of the centra. If the temperature of 
the centrum rises so far that it enters the permanent phase region 
of temperature, then the substance begins to respond — previous 
excitation being understood — just as if the whole “phosphor” had 
been brought to the higher temperature. When the stored charge is 
used up, darkness follows the glow,, and it is extinguished. It has 
also been already shown that when ultra-red light is the acting 
agent a different local molecular rise in temperature belongs to each 
band, also to those of the same “phosphor”, and that each active 
metal has a particular distribution of extinguishing powers over the 
spectrum. Discussion of these characteristics in themselves will be 
reserved for a special communication; our main wish for the present 
has been to concentrate our attention upon the confirmation and 
extension of these views which have been developed from the results 
of observations obtained at very low temperatures. 
Corresponding with the great charge which is kept stored at 
low temperatures, the response to ultra-red at these temperatures 
is also very intense. As a general rule in this case the actual 
lighting up is far more striking than the subsequent extinction which 
here takes place far more slowly than at ordinary temperature. We 
may just now instance the extreme case of zinc sulphide, in 
which the lighting up which always precedes extinction (“1909”) 
escaped the notice of even a careful observer *). If one allows 
ultra-red light to act upon zinc sulphide in liquid hydrogen, one 
observes a glow during many seconds 3 ). As other examples of 
response to ultra-red in liquid hydrogen we may name: Ba Bi K, 
extremely intense and remaining green with the a 3 and ft band, 
hence like the afterglow at ordinary temperature, BaCuLi very 
clear,. red, band, hence like the glow at ordinary temperature; 
and similarly Sr Bi Na with clear bluish-green responsive glow. To 
b Also P. Lenard and Sem Saeland loc. cit. note 2. p. 164. 
2 ) A. Dahms, Ann. d. Phys. 1903. 
3 ) The colour is first green, and then reddish. By projecting a spectrum on the 
“phosphor” immersed in solidifying hydrogen we have found that the red responsive- 
glow lies more in the proximate part, the gr?en more in the ultra-red of the 
spectrum. 
