322 



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the L series for this element. A value of 42.2 volts was deduced for 

 the quantum equivalent of the shortest member of the L series for 

 boron. 



Carbon 



With carbon critical potentials were observed at 33 volts and 

 72 volts. Some difficulty was experienced in interpreting these results. 

 Millikan^ in photographing the extreme ultra-violet spectrum of 

 carbon found that it terminated at X 360.5^. This, he concluded, 

 was the shortest member of the L series of the element. As the 

 quantum equivalent of X 360.5 A is 34.2 volts, it would seem natural 

 to interpret the potential of 33 volts as corresponding to the limiting 

 frequency of the L series. This interpretation would, however, leave 

 the critical potential of 72 volts unexplained. The potentials 33 volts 

 and 72 volts were therefore tentatively assumed to represent the 

 first and last members of the L series for carbon, an assumption which 

 fitted in with the interpretation given above for the critical potentials 

 found for lithium, beryllium and boron. 



Tab4e II contains the values of the critical potentials found in 

 this part of the investigation together with values found with the 

 ionisation method for other elements by either Kurth or Mohler and 

 Foote. The Table also contains the atomic numbers of the elements, 

 the square roots of the critical potentials and the quantum equivalent 

 wave-lengths of these potentials. 



TABLE II 

 Critical Voltages and L Series Wave-lengths 



iMillikan. Ast. Phys. Jl., Vol. LII, No. 1, p. 61, July, 1920. 



