PHYSICS: H. S. UHLER 
89 
obtained lead to wave-lengths which show a systematic deviation from 
the experimental data. In other words, a 'smooth' curve can be drawn 
through the points having as abscissae the atomic numbers and as or- 
dinates the corresponding percentages by which the calculated wave- 
lengths are algebraically greater than the experimental values. The 
extreme deviations are +2.00%, -0.62%, and + 0.46% for Zn, Ce, 
and U, respectively. Since the glancing angles are said to be correct 
within 0.3% it follows that the extreme interval of deviation (2.62%) 
must be real and that Moseley's law does not hold exactly over the en- 
tire range. In the case of the L-^i series for which 46 wave-lengths 
from arsenic {N = 33, X = 9.449 A) to uranium (X = 0.720 A) are 
given, another smooth curve of departure is obtained, the extreme de- 
viations being +13.35%, —3.06%, and + 5.84%, corresponding to As, 
Nd, and U, in the order named. The range 16.41% certainly cannot 
be accounted for as due only to experimental error. The data for the 
L-ji series extend from zirconium {N = 40, X = 5.386) to uranium 
(X = 0.615) and comprise 36 wave-lengths. The deviations for the 
associated curve of departure are found to be +9.22%, —1.68%, and 
+3.96% for Zr, Yb, and U, respectively. Unfortunately, only a por- 
tion of the literature relating to the K series is at present accessible to 
me. Nevertheless, the 20 wave-lengths of the means of the K-ai and 
K-a2 series extending from sodium (N = 11, X = 11.951 A) to ger- 
manium (N = 32, X = 1.259 A), exhibit departures from the linear rela- 
tion which are greater than the probable errors of the experimental 
numbers. In this case the original investigators state, and also give 
data to show, that the wave-lengths for the same line obtained from dif- 
ferent negatives agree to within 1 or 2 tenths of one per cent. Just 
as for the Z-series, so here, the curve of departure with respect to the 
linear law deviates more and more as the smallest atomic number is 
approached. The deviation for magnesium was found to be +0.41%, 
and for sodium +0.74%. The answer to the first question is, therefore, 
that Moseley's law does not hold for the entire range of the L-series 
and that it seems to be slightly inexact for the most intense lines of the 
K-series. 
The second question proposed may be answered at once. The em- 
pirical equation 
VV^ = A+ BN + C{D + N)-' 
was found to represent the L-series well within the limits of experimental 
error even when the values of the parameters a\ h' , C, and D were ob- 
tained by graphical processes and not by the method of least squares. 
