Vol. 8, 1922 
PHYSICS: L. W. MCKEEHAN 
273 
number, whereas Ca, the only member of the second three which has been 
analyzed, has cubic symmetry.^* The remaining element in this column, 
Hg, has rliombohedral symmetry. 
The oxide, BeO, finds an analog in ZnO, all the other monoxides in the 
column having cubic symmetry, except HgO which forms monoclinic 
crystals. The structure of ZnO has been reported by W. L. Bragg^^ to 
be hexagonal close-packing of molecules with c/a = 1.608 and a = 3.22 
X 10 cm. Recent data obtained by HedvalP^ but not reduced by him 
is in good agreement with this structure. Bragg regards the two hexagonal 
lattices of the proposed arrangement as determining the positions of the 
zinc atom-centers, and suggests that the oxygen atom-centers lie at the 
points of two similar lattices derived from these by displacing both of them 
along the hexagonal axis by about Sc/S. The same type of structure is at 
TABLE II— BeO 
ESTIMATED 
MEASURED 
COMPUTED 
ATTRIBUTED 
COMPUTED^ 
INTENSITY 
2r9 IN CM. 
LOG (lOM) 
TOl 
LOG (10%) 
2 
4.69 
0.4911 
J/3 
1 
5.43 
0.4277 
X 
8 
6.23 
0.3685 
(10.0) 
0.4310 
6 
6.67 
0.3392 
(00.2) 
0.4301 
10 
7.09 
0.3128 
(10.1) 
0.4297 
1 
7.57 
0.2847 
X 
3 
9.15 
0.2035 
(10.2) 
0.4311 
8 
10.90 
0.1290 
(11.0) 
0.4300 
8 
11.89 
0.0923 
(10.3) 
0.4308 
4 
(20.0) 
6 
12.86 
0.0593 
(11.2) 
0.4303 
4 
(20.1) 
i 
(00.4) 
4 
(20.2) 
4 
(10.4) 
2 
16.40 
1.9582 
(20.3) 
0.4293 
1 
16.90 
1.9459 
(21 .0) 
0.4309 
1 
17.29 
T.9366 
(21.1) 
0.4303 
4 
(11.4) 
5 
(10.5) 
2 
18.34 
T.9126 
(21.2) 
0.4304 
4 
(20.4) 
1 
19.35 
T.8911 
(30.0) 
0.4305 
2 
20.04 
1.8770 
(21 .3) 
0.4298 
Mean 
0.43032 
Result a = 
2.696 X 10-8 cm 
^ All planes theoretically capable of reflection within the range of the tabulated values 
of 2re are included. * 
2 Computed for c/a = 1.63. 
^ X = impurity. 
^ Not observed with certainty. 
5 Forms with next an irresolvable doublet (As = 0.01 cm.). 
