484 
AMERICAN JOURNAL OF BOTANY 
[Vol. 9, 
energy to pass through to the photographic film would be approximately 
twice as thick as the most efficient salt tablet. 
Eastman's duplitized X-ray films were used, two films being used for 
each exposure. The two films made it possible to observe very faint lines 
which would not be distinguishable on a single film. 
Test Reflections 
In order to test the apparatus, sodium chloride was used first, for its 
crystal structure has already been worked out and it is known to produce 
lines readily by this method. An exposure of 4 hours, at 40,000 volts and 
4 milliamperes current, produced the lines shown in figure 4. 
654332211 112233456 
aaaaj3a^a(3 ^ajSa^aaaa 
Fig. 4. Sodium chloride, positive print. Reflected lines are light. 
If these lines corresponded favorably with their calculated position, then 
the apparatus could be expected to produce lines from other crystal powders. 
Also the denser lines, those numbered i^, 2^, etc., should correspond with 
the theoretical position of the lines made by reinforcement of the waves 
having a .617 A. wave-length; and the fainter lines, numbered i^, 2^, 3^, 
should be in the positions where reinforcement occurs of the waves having 
a .533 A. wave-length. The latter carry much less energy and would 
therefore make fainter lines. 
Tables i and 2 give the results of measurements of the glancing angles, 
and of the computations based on the equation, \ = 2d sin 6, which shows 
Table i. Lines Produced hy Sodium-chloride Powder; Rhodium Anticathode; X = .617 A. 
Distance 
No. of 
Line 
Distance 
between 
between 
Glancing 
Atomic 
Indices 
Lines 
Angle 
0* 
Sin d 
Planes 
d 
Ratio 
of 
a Lines 
(mm.) 
2 \smd J 
Calculated 
Planes 
I 
61.5 
6° 18' 
.10973 
2.81 A. 
... A. 
1. 00 
100 
2 
87 
8° 54' 
•I5471 
1.99 
1.99 
.707 
no 
3 
107 
10° 57' 
.18995 
1.63 
1.62 
.577 
III 
4 
122.5 
12° 32.5' 
14° 7' 
15° 34' 
.21715 
I.4I 
1. 41 
.500 
loof 
5 
138 
.24390 
1,26 
1.26 
•447 
210 
6 
.26836 
I-I5 
I-I5 
.408 
211 
* The film, when in the film-holder, lies on the circumference which subtends all of the 
glancing angles. By construction, i ° on this circumference equals 2.44 mm. 
t This line is the result of reflection of the second order from the 100 planes; and here, 
d should be exactly ^d as obtained from the reflection of the first order from those planes. 
