PHYSICS: DUANE AND PATTERSON Proc. N. A. S. 
lines for chemical elements of higher atomic numbers than that of tungsten 
with our spectrometer. Hence we cannot make a direct comparison be- 
tween emission and absorption wave-lengths obtained under the same 
experimental conditions for these elements. If we take the wave-lenghts 
recorded by Siegbahn and Friman,^ we find that (a) our value for the 
absorption wave-length, La^, is shorter than that of the emission line, 74, 
for each element and that the difference between the two increases slightly 
with the atomic number; {h) our value for the absorption wave-length, 
TABLE 1 
Critical Absorption Wave-Lengths. L Serirs of X-Rays 
Grating Space for Calcite, 2d = (6.056 ±0.004) X lO'^ cm. 
CHEMICAL 
ELEMENT 
ATOMIC 
NUMBER 
ABSORBING 
SCREEN 
MEASURE 
BY 
WAVE-LENGTHS, X X 108 CM. 
La\ Lai Lai 
Tungsten 
74 
de Broglie 
1 
217 
1 
083 
Tungsten 
74 
Na2W04 
Author's 
1 
2136 ±1 
1 
0726 ±5 
1 
024 ±3 
Platinum 
78 
Wagner 
1 
072 
0 
934 
Platinum 
78 
de BrogHe 
1 
069 
0 
930 
Platinum 
78 
Metal 
Author's 
1 
0705 ±3 
0 
9321 ±3 
0 
8885 ±9 
Gold 
79 
Wagner 
1 
042 
0 
914 
Gold 
79 
de Broglie 
1 
038 
0 
898 
0 
858 
Gold 
79 
Metal 
Author's 
1 
0383 ±3 
0 
8993 ±3 
0 
8606^8 
Mercury 
80 
de Broglie 
1 
006 
Mercury 
80 
HgS04 
Author's 
1 
0067 ±5 
0 
8700 ±3 
0 
8335 ±9 
Thalium 
81 
de Broglie 
0 
974 
0 
840 
Thalium 
81 
T1.(S04)3 
Author's 
0 
9776 ±3 
0 
8415±3 
0 
8055 ±14 
Lead 
82 
de Broglie 
0 
945 
0 
811 
Lead 
82 
Pb(N03)2 
Author's 
0 
9497 ±3 
0 
8133 ±3 
0 
7803 ±9 
Bismuth 
83 
de Broglie 
0 
921 
0 
786 
0 
753 
Bismuth 
83 
Metal 
Author's 
0 
9216±3 
0 
7872 ±3 
0 
7532 ±9 
Bi(N03)3 
Radium 
88 
de Broglie 
0 
802 
0 
670 
Thorium 
90 
de Broglie 
0 
757 
0 
624 
0 
604 
Thorium 
90 
Th(S04)2 
Author's 
0 
7596 ±3 
0 
6286 ±3 
0 
6044 ±7 
Uranium 
92 
de Broglie 
0 
718 
0 
588 
0 
564 
Uranium 
92 
Acetate 
Author's 
0 
7214=t=3 
0 
5918±3 
0 
5685 ±7 
La2, is longer than that of the emission line, 72, for tungsten and gold, but 
shorter for the other elements; (c) our value for the absorption wave- 
length, Lgi, is longer than that of the emission line, (So, for tungsten, gold, 
and thallium, but shorter for platinum and bismuth. The relative posi- 
tions of these emission and absorption lines appear to be matters of con- 
siderable theoretical importance,^ and this subject will be discussed at 
greater length in a future note. 
The Wave-lengths as Functions of the Atomic Numbers. — Many of the 
laws connecting X-ray wave-lenghts with each other, or with the atomic 
numbers of the chemical elements may be expressed most simply in terms 
