60 
PHYSICS: DA VIS AND TERRILL 
Proc. N. a. S. 
Measurements were made on the whole spectrum, line and continuous. 
The relative heights of the peaks of the curves for the two lines after proper 
correction for the natural leak and the continuous spectrum was taken as 
the relative intensities of the lines in the several orders. Readings were 
carefully made on each side, left (ly) and right (R) of the zero position of 
the crystal. The expression ^/i^h ~ R — 180°) is then the mean grazing 
angle Q for the particular line and order. 
The results are given in the table. The spectra of certain orders were 
so weak and the curve so flat that it was not possible to fix the position 
of the peak with sufficient accuracy to be of value in the calculation of 
the grating space. 
The relative intensities of the and jSi lines are given in the table. 
The odd orders are stronger than the even orders as observed by de Broglie. 
The third and fifth orders are stronger than the first. Radiation at higher 
orders than the 7th was observable. 
The grating space d calculated for the two lines is given in the table. 
The values agree fairly well with those calculated by Seigbahn {Phys. 
Rev., Sept., 1916) from the measurements made by Gorton {Phys. Rev., 
March, 1916), for certain lines in the L radiation of tungsten. 
It is noticeable that the grating space as here determined increased with 
increasing spectral order. The results calculated by Seigbahn from 
Gorton's measurements show the same tendency. This effect has also 
been noted by W. Stenstrom (Untersuchengen der Rdntgen Spektra, 
Lund, 1919). Stenstrom attributes this progressive change in the apparent 
value of J to a very small refraction of the X-rays in the crystal. This 
is a possible explanation of the effect but not the only one. It may well 
be due to small curvature or irregularities in the crystal. One can readily 
show that if the reflecting planes do not line accurately at the center of 
rotation of the crystal, or if the beam of X-rays from the slits do not pass 
accurately across this center of rotation, there will be a progressive change 
in the calculated values of d for the various orders if the crystal planes have 
even a small curvature. The direction of the change of d with order will 
depend on whether the crystal is convex or concave. 
TABLE 1 
N 
jSi LINE 
ai LINE 
INTENSITY 
e 
d 
8 
d 
01 
• 1 
l°-50'-50" 
9.87 
2°- 4'-0" 
9 
.845 
100 
364 
2 
3-39-38 
9.914 
4- 7-7.5 
9 
.885 
68 
221 
3 
5-3-30 
9.891 
6-10-15 
9 
901 
154 
544 
4 
8-13-15 
9 
931 
45 
175 
5 
9-8-38 
9.957 
10-16-38 
9 
949 
136 
508 
6 
9.1 
28 
7 
14-27-0 
9 
958 
32 
101 
