5i8 
PHYSICS: DUANE AND PATTERSON Proc. N. A. S. 
certain difficulties (discussed by Sommerfeld in his book) that we encoun- 
ter, if we suppose that the orbits all lie in the same plane. Possibly these 
difficulties will disappear, when we study more thoroughly atomic models 
in which the orbits do not lie in the same plane. 
1 E. Wagner, Ann. Physik, Leipzig, March, 1915 (868). 
2 M. de Broglie, /. Physique, Paris, May-June, 1916 (161); and Paris C. R. Acad. 
Sci., Nov. 24, 1919 (962). 
^ Blake and Duane, Physic. Rev., Ithaca, Dec, 1917 (624); and Duane and Patterson, 
Ihid., 1920. 
'I Siegbahn and Friman, Phil. Mag., London, April, 1916 (423); and Nov., 1916- 
(497). 
^ D. L. Webster, Proc. Nat. Acad. Sci., Washington, D. C, Jan., 1920 (26). 
^ Duane and Hu, Physic. Rev., June, 1918 (488); and Dec, 1919 (516); and Duane 
and Shimizu, Ibid., Feb., 1919 (159) and Dec, 1919 (522). 
^ Duane and Shimizu, Ihid., July, 1919 (67); Duane and Patterson, Ihid., 1920; 
Duane and Stenstrom, Ihid., April, 1920 (302); and Proc. Nat. Acad. Sci., Aug. 1902. 
^ Stenstrom, Doctor's Dissertation, Lund, 1919. 
9 Webster and Clark, Proc. Nat. Acad., March, 1917 (181). 
10 Rubinowicz, Physik. Zs., Leipzig, 19, 1918 (441-465). 
11 Bohr, Copenhagen Academy, 1918. 
12 Compare Sommerfeld, Atomhau und Spektrallinien, Chapter 6. 
13 Compare de Broglie Paris, C. R. Acad. Sci., Nov. 24, 1919 (962). 
ON THE RELATIVE POSITIONS AND INTENSITIES OF LINES 
IN X-RAY SPECTRA 
By WiIvLIAm Duane and R. A. Pattejrson 
Jefferson Physical Laboratory, Harvard University 
Communicated August 17, 1920 
Grouping of L Series Lines. — The wave-lengths of the lines in the L 
series of X-rays have been measured for a great many of the chemical 
elements by Siegbahn and Friman.^ They have published graphs which 
represent the square roots of the frequencies of corresponding lines in the 
spectra of different elements as functions of the atomic number. The 
graphs for the lines 1, a2, ai, ^2 and ^5 are very nearly straight, indicating 
that the square roots of the corresponding frequencies are almost linear 
functions of the atomic numbers, whereas the graphs for the other lines 
are curved, indicating a marked departure from the linear law. This 
would seem to mean that we can divide the lines in the L series into at 
least two groups. 
In his work on characteristic absorption de Broglie^ found three critical 
absorption wave-lengths associated with the L series of gold, bismuth, 
thorium and uranium. The authors^ have extended this, and have mea- 
sured the third critical absorption wave-length as well as the other two for 
the elements they examined from tungsten to uranium both inclusive. The 
fact that three critical absorption wave-lengths appear in the L series of 
