Vol. 6, I920 PHYSICS: DUANE AND STENSTROM 481 
TABLE 1 
K Series of Tungsten 
n\ = 6.056 X sin 6* X IQ-^ cm. 
X X 108 em. 
ORDER, n, OF 
SPECTRUM 
as 
T 
ABSORPTION 
1 
0.18441 
0.17898 
0.17833 
2 
0.21342 
0.20850 
0.18415 
0.17880 
0.17810 
3 
0.21339 
0.20848 
0 . 18420 
0.17909 
0.17795 
4 
0.215 
0.21341 
0 . 20862 
0.18418 
0.17905 
5 
0 . 20862 
Weighted 
Means 
0.215±1 
0.21341±3 
0.20860 ±4 
0.18420 ±3 
0.17901 ±6 
0.17806^7 
Last Year 
0.2134 
0.2087 
0.1842 
0.1785 
Siegbahn 
0.21345 
0.20878 
0.18430 
0.17934 
1 
X 
4.65 
4.6858 
4 . 7938 
5.4290 
5.5863 
5.6160 
V 
4239. 
4270 . 3 
4368.7 
4947.4 
5090.9 
5118.0 
The seventh Hne in the table contains the weighted mean values of the 
wave-lengths, together with a rough estimate of the precision of the 
measurements. The 7 wave-length is more difficult to measure than 
the others owing to the fact that the critical absorption wave-length 
lies so near it. The target of the X-ray tube absorbs some of its own rays. 
In order to estimate the absolute accuracy of the wave-lengths we must, 
of course, as in all work in X-ray spectra, take account of the errors in 
the grating constant of the reflecting crystal. These appear to add up 
to about 0.06%. (See a "Report on Data Relating to X-Ray Spectra," 
published by the National Research Council.) 
For purposes of comparison we have added, in the eighth and ninth 
lines, respectively, the values obtained last year by the ionization method 
{Physical Review, July, 1919, p. 67) and those given by Siegbahn {Phil. 
Mag., Nov., 1919, p. 639), which he measured by photographic methods. 
A small correction (Vsooo) has been made in these wave-lengths corre- 
sponding to the value of the grating constant of calcite we use. 
In order to test general relations between the wave-lengths and also 
theoretical equations it is convenient to have at hand the wave-numbers, 
1/X, and the ratios, v/v^, of the frequencies, v, to the fundamental 
Rydberg frequency, v^. In calculating these ratios we have used the 
Rydberg fundamental wave-number, = 109737, calculated for heavy 
atoms from the data obtained by Paschen in the spectra of hydrogen 
and helium. Line 10 in table 1 contains the values of 1/X, each divided 
by 10^, and line 11 contains the values of v/v^, calculated from our values 
of X. 
The critical absorption wave-lengths appear in the last column of table 
