Energy Distribution in Spectra. 



59 



Holtsmark *, using a Wehnelt lime cathode, proved that 

 H0/H a is independent of the voltage between 52 and 

 600 volts, and is also independent of the current strength, 

 but changes with pressure. 



These results of Vegard and Holtsmark strongly support 

 the conclusion mentioned above. Confirmatory evidence 

 in the case of other spectra appears from the work of 

 McLennan 1", who has shown that in the spectra of mercury, 

 cadmium, zinc, and magnesium caused by an electric dis- 

 charge, the complete spectrum appears suddenly when the 

 exciting electrons attain definite velocities. The author 

 does not wish to exclude the possibility that under certain 

 conditions electrons may possess such energy that they may 

 excite one line only of the Balmer series, but takes the view 

 that in a luminous discharge the great majority of the 

 radiating atoms have been ionized and give out light owing 

 to subsequent recombination. The method of ionization is 

 taken to be immaterial as regards the distribution of light 

 in different wave-lengths during such recombination. 



The intensity distribution will, however, be affected by the 

 mean free path of the luminous atom and the nature of 

 the molecules in its vicinity whose fields of force act on it. 



It follows from Bohr's theory that the diameter of the 

 hydrogen atom, and hence its mean free path, will vary as 

 the hydrogen electron passes from one ring to another. 

 Table 5 -shows the results calculated for hydrogen atoms 

 moving in water vapour at a pressure of 1 mm. 



Table V. 

 Luminous Hydrogen atom in Water Vapour. 



No. of King 



1 



2 



3 



4 



5 



6 



10 



Diameter of atom 1 

 incms.XlO 8 . J 



1-34 



5-36 



1206 



21-4 



33-5 



48-2 



67 



Mean free path 1 

 in cms. at 1 mm. 1 



9-9X10" 3 



3-5xl0~ 3 



1-25 X 10 ~ 3 



5-05 X 10 " 4 



2-36 x 10 " 4 



1-23 X 10 " 4 



1-78X10" 5 



pressure. J 

















Let E a , Ep .... be the energies which would be emitted 

 per unit number of luminous atoms per second in the lines 



* Phys. Zeit. June 15, 1914, pp. 605-7. 



t Proc. Koy. Soc. A. xci. pp. 485-492 ; A. xcii. pp. 305-313, 574-584. 



