( 173 ) 
become less sharply defined. The same remark may be applied to 
the excitation- and extinction-distributions l 2 ). 
§ 9. On the upper temperature limits to the excitation of phosphor¬ 
escence by light, and on the glow of “phosphors” when heated in 
flames, or ivhen crushed at high temperature. It seems of importance 
to us to remark that our demonstration of the existence of phos¬ 
phorescence, and particularly of the storing of electrons when the 
temperature sinks to 14° K., also taken in connection with an earlier 
research s ), affords a proof that the photoelectric action at low tem¬ 
peratures remains unchanged even down to this very low tempera¬ 
ture. This proof was first given by Lienhop 3 ), of the Kiel Laboratory, 
for temperatures sinking to close upon that of liquid air, from which 
the validity for all temperatures followed with the highest probability; 
and for high temperatures Millikan and Winchester 4 5 ) and Ladenburg 6 ) 
have given important direct confirmations. It seems therefore to be 
beyond doubt that the ejection of electrons by atoms in response to 
excitation by suitable wave-lengths takes place at all temperatures; 
and it must, therefore, be explained why the phosphorescence in 
response to light excitation of the alkaline earths cannot be noticed 
above a definite high temperature. 
It has already been shown that this upper limit to the induction 
of phosphorescence by light lies lowest in the Ba-“phosphors” and 
higher in the Sr- and Ca-“phosphors” — e.g. in BaBi^? at 170° C., 
in Sr Bi £ above 300° C., and in Ca Bi ft a little above 500° C. — 
and that it, however, is in no case a sharply defined temperature, 
but that at high temperatures the excitability by light slowly 
ceases (“1904” p. 452). The observation has later been added ®) 
that it is just in the neighbourhood of this limit of temperature 
that the “phosphors” begin to conduct electricity. If we assume that 
this conduction is electrolytic, then it is an obvious deduction that 
the presence of electrolytic ions prevents the excitation of phos¬ 
phorescence by light, perhaps through the circumstance that the lost 
electrons are brought back to the metallic atoms which have been 
rendered positive by their ejection of electrons under photoelectric 
J ) The latter according to ‘1909” should offer the first chance of the resolution 
into a group of lines. 
2 ) P. Lenard and Sem Saeland. Ann. d. Phys. 28 p. 476 1909. 
8 ) A. Lienhop, Ann. d. Phys. 21 p. 211, 1906. 
4 ) Milukan and Winchester, Phil. Mag. July 1907. 
5 ) E. Ladenburg, Verh. d. d. phys. Ges. 9 p. 165 1907. 
6 ) P. Lenard and Sem Saeland, Ann. d. Phys. 28 p. 498, 1909. 
