Physics. — G. Hkktz- "-On the Mean Free Ptith of Sloiu Electrons 

 in Neon and Argon." (Comtininicated hy Prof. P. Ehkknfkst). 



(Communicated at the meeting of March 25, 1922). 



The reason for iiiidei taking these measurements was given bj 

 researches concei-ning the efïiciency of non-elastic impacts of electrons 

 ill neon an(i ai'gon at potentials jnst above the excitation-potential. 

 It is known, that those collisions between electrons and the atoms 

 of rare gases, which take |)lace below the excitation-potential 

 characteristic for each gas follow the laws of elastic collisions. As 

 soon as I he kinetic energy of an election surpasses the value 

 corresponding to the excitation potential, it can, on collision with 

 an atom, transfer energy to the latter and thereby raise it from its 

 normal state to a higher quantum-state. This, however, does not take 

 place at every collision between a sufficiently fast electron and an 

 atom; only a certain |)art, in the case of rare gases most probably 

 only a small fraction, of these collisions is non-elastic and causes 

 excitation of the colliding atom. This fraction we call the efficiency 

 of the particular non-elastic impact. It is equal to the probability 

 that an iuipact of an electron possessing the required energy really 

 leads to a transfer of energy. It is naturally a function of the 

 velocity of the electron. The form of this function however is not 

 yet known. 



In a glow-discharge the two rare gases neon and argon show a 

 characteristically different behaviour, which among other things 

 manifests itself under similar circumslances l\v producing in neon 

 a much more intensive emission of light than in argon. The reason 

 for this different behaviour according to G. Holst and E. Oosterhuis ') 

 probably lies in the fact, that in argon electrons having a velocity 

 above the excitation-potential readily transfer their kinetic energy 

 to the argon-atoms thereby exciting the emission of ultraviolet rays 

 (resonance), while in neon only a small fraction of the impacts leads 



^) G. Holst and G. Oosterhuis, Physica. 1, 78, 1921. 



