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BELL SYSTEM TECHNICAL JOURNAL 



lower of the continuous straight lines coming downward from the right 

 is the prolongation of the K line from the heavier elements downward; 

 the upper is the prolongation of the Ka line. The fact that these inter- 

 sect pro\es that linear extrapolation from the range of heavier atoms 

 is unjustifiable. 



Re\-erting to the graph in Fig. 10, iliu pmlikMii of properly extra- 



Fig. 1.^— K.xcitation-potciitials currclaU-il witli .1/ electrons. (Philosciphkal 

 Magazine.) 



polating the L and M curves is clearly not so simple as it was for the 

 K curve; since they extend over shorter segments and do not come so 

 far down into the range of light elements. In Fig. 12 (from McLennan 

 and Clark) the circles for the elements from number 3 to number 17 

 represent observed excitation-potentials which they attribute to 

 displacements of /, electrons; those for the elements from number 30 

 to number ()'.) represent ihe highest ami the lowest recorded emission- 



