186 



so that the methods of the collisions of electrons is not sufficient to 

 separate them, only a "continuous spectrum" can be observed. When 

 the curve given in fig. 3 is compared with this, the serial system 

 is clearly found back in it. 'J'he tiivst maximum corresponds to the 

 gi-oup of the quantum transitions 0.5.9 — ^l,5.v, the second to the group 

 0.5.9 — -2 />, and then at a distance of 1 Volt follows the s|)ectrum 

 of the transitions to higher quantum conditions, which seems conti- 

 nuous on account of the small dissolving powei-. Also quantitative 

 the agreement is good, as is seen in tig. 8, where the quantum tran- 

 sitions observed with collisions of electrons have been indicated by 

 arrows, of which the projection on the axis of abscissae is equal to 

 the observed value of the |)Otentials of excitation resp. ionization. 

 It is, therefore, seen that the serial scheme of neon has become 

 complete by the addition of the term 0.5 5 = J 79800 =t 1000. 

 There is no room in this serial system for a resonance-potential 

 of 1J.8 Volts and ionization-polentials at 16.7 and 20 Volts, which 

 values were deiived l)y Horton and Davies ^) from their experiments, 

 nor was there any indication at all in my measurements of the 

 occurrence of resonance or ionisation at these potentials. On the other 

 hand the experiments of the same investigators on excitation of 

 light in neon through collision of electrons ^) are in good agreement 

 with the conclusions which may be derived from the conqileted 

 scheme. As can at once be read from the figure, the lines of the 

 principal series must first appear alone starting from 19.2 Volts, 

 then from about 20.2 Volts the lines of the secondary series must 

 gradually begin to make their appearance, while the whole spectrum 

 otdy can be emitted above the ionizatión-potential. Horton and 

 Davies actually found that at 20 Volts only the lines of the principal 

 series were emitted, the whole spectrum not appearing before 22.8 Volts. 



It would be of importance to ascertain whether there may perhaps 

 be terms for neon that correspond to metastable states, as Franck 

 has found them for helium and mercury"). To find this out it would, 

 however, be necessary really to separate the different terms, and 

 for this the dissolving power of the method of the collisions of the 

 electrons is not yet sufficient. Measurements with the usual arrange- 

 ment for showing photo-electric radiation proved, as was to be 

 expected, the occurrence of photo-electrically active radiation at 

 both the excitation potentials observed. 



As was already stated above, in argon there likewise appear two 



1) F. Horton and A. G. Davies, I.e. 



2) F. Horton and A. G. Davies, Phil. Mag. 41, 921, 1921. 



3) J. Franck, Phys. Zeitschr. 22, 388, 1921. 



