Vol. 8, 1922 
PHYSICS: DUANE AND PATTERSON 
89 
elude two more M absorption frequencies for U and Th, and the first three 
M Hmits for Bi. Table V contains his values with the exception of L3 — 
M3 for Bi which we have corrected to accord with our new value of L.3 
for that element. 
In each case the emission frequency exceeds the difference in absorp- 
tion frequencies, but by an amount that is less than 0.3 of a per cent. 
The K Series of Molybdenum. — The authors have also measured the 
emission and absorption spectra for the K series of molybdenum. The 
apparatus and method used are described in previous papers.^ A Coolidge 
tube equipped with a molybdenum target and an extra arm at the end of 
which happened to be a thin glass window served as the source of ra- 
diation. 
Table VI contains the results of these measurements. 
TABLE VI 
K Series of Molybdenum 
Grating Space of Calcite 
= 2d ^ 6.056 (10) -'^ Cm. 
L,IME 
NO. 
GLANCING ANGLE 
WAVE-LENGTH X (10)8 CM. 
ORDER 
«2 
3 
13°-36'-08" 
0.71213 ± 8 
2d 
«1 
3 
13°-31'-07" 
0.70783 =fc 7 
2d 
/3' 
3 
12°-02'-50" 
0.6320 ± 2 
2d 
/3 
6 
12°-01'-50" 
0.63114 =t 7 
2d 
1 
5°-59'-05" 
0.6314 ± 3 
1st 
7 
3 
ll°-48'-32" 
0.6197 ± 2 
2d 
7 
1 
5°-52'-30" 
0.6199 ± 3 
1st 
K 
1 
5°-51'-40" 
0.6184 ± 2 
1st 
In the second column the number is the number of actual measurements 
made. 
In the second order, the /3 line was markedly asymmetrical and we were 
able to estimate the position of its weaker component, (3', predicted by 
Sommerfeld. The wave-length difference between these two lines is of 
the same order of magnitude as that found in the case of other elements. 
The wave-lengths of ^ and 7 found in the first order are definitely longer 
than those found in the second order. This is chiefly due to the complex 
structure of both of these lines, although several investigators including 
the authors have found a similar but smaller effect in the case of emission 
lines supposed to be single. 
In a recent paper Overn^^ has also given wave-lengths for these same 
emission lines. His values, however, do not agree with ours even when 
corrected for the difference between the rock salt grating space used by 
him and the calcite grating space used by us. The discrepancy between 
his values and ours seems to increase as we go farther from the "white 
line" used as a reference line by him. 
As we determined these wave-lengths b}^ the ionization method, we are 
also able to give the ratio of the intensities of ai and ao. From three de- 
