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PHYSICS: WEBSTER AND CLARK 
parallel with a greater slope than the four. This suggests that the four, 
oLi, ^2, and 185, (see fig. 1) form one series, which we shall call Li, 
while the others, rj, (3^, (Ss, 71, 72, 73, and 74, form another series, L2. 
The Li series is remarkably similar in appearance to the K series, un- 
less we include in it the line /, reported by Siegbahn in a paper which 
is not yet accessible, but which is quoted by Friman.^ From this sim- 
ilarity one would expect the Li series to have a critical potential equal 
to the quantum potential of its highest frequency member, /^s. The L2 
series, on the other hand, is totally different in appearance so that sim- 
ilar predictions can scarcely be made. The existence of two series 
accounts readily for that of two discontinuities of absorption. 
Following farther the analogy with the K series, one might expect 
all lines of each of the Li and L2 series to increase in intensity by the 
same ratio with any given increase of potential,^ and we may expect 
their intensity-potential graphs to be concave upward, while that of 
general radiation of any one frequency starts concave downward and 
soon becomes linear.'^ 
