( 1114 ) 
Physics. — “/onization of gases by light, emitted from GrissLEr 
tubes. Research after the existence of selective effects in the 
wonization.” By H. G. Cannecinrer. (Communicated by Prof. 
W.H. Junius). 
Since HaLLwacus’*) discovery that an insulated, negatively charged 
zincplate loses its charge, when ultra-violet light falls upon it, this 
property of the ultraviolet light has been a subject of research to 
many observers. Several solids and liquids prove photoelectric, i.e. 
when exposed to the light they send out negatively charged particles, 
whereas they acquire a positive charge themselves, if they were 
uncharged at first. 
On gases too the ultra-violet light has an influence. When the 
light shines through them, they acquire conductivity ; the light ionizes 
the gasmolecules. 
If we put the question, how we are to figure the action of the 
ether-vibrations on the molecules of substances, which led to the 
loosening of negatively charged particles from them, we are inclined 
to take it for an effect of resonance. If the molecules of the sub- 
stance, solid, liquid or gas, on which the light is snining are struck 
by vibrations, the period of which corresponds to those which the 
electrons in the molecules can emit themselves under certain circum- 
stances, then the electrons will by resonance get so strong a motion, 
that they are loosened from the molecule and will behave like free 
particles. 
From this point of view we may expect that, if a given substance 
in the luminous state emits electrically acting vays, this same sub- 
stance, when struck by these particular rays, will be more photo- 
electric, than when it is under the influence of rays from any other 
source of light; also we may take for granted that, examining the 
effect of the radiation, emitted from the above mentioned source 
of light, on different substances, including the substance emitting the 
active rays, the effect on this latter substance, when compared 
to that on the other substances under examination, will be found 
the strongest. 
If we use as sources of light discharge tubes filled with different 
gases, and examine the ionization excited by the light in the same 
gases, then it will be possible for us to arrange them in a detinite 
order, according to the measured effect, which order will depend 
1) Wied. Ann. 33, 801, 1888. 
