644 
PHYSICS: F. C. HOYT 
Proc. N. a. S' 
The evidence in these pictures would seem to put 72, 73 and 75 in L3, 
as they show well at 12.5 kv., but are out at 12. They are still weaker, 
however, than /S? which is very faint near its critical potential, so it is 
possible they would not show at 12 kv. even if belonging to L2. 
^s, ^9 and 77 are too weak to show except at high voltages. 
The behavior of the other lines that have already been classified is what 
would be expected. The change in intensity ratio of /3i and ^2 is particu- 
larly noticeable. They are nearly the same at 13 kv., but 'quite different 
at 12. 7i behaves as would be predicted. 
In some of the pictures the absorption limit of tungsten, due to absorp- 
tion in the anticathode, shows near jSs, and there is also one near (32. This 
latter has exactly the wave-length of Zinc Ky and is probably due to zinc 
in the glass of the tube. The light spot showing in the region between 
7i and /Ss is an imperfection in the crystal. 
The classification of the lines, to date, is as given below. Those for 
which further work is necessary are marked with a question mark. 
Li /, a2, (Xi, ^2, /55, ^7 
L2 7], 71 
Ls /33, /34, 72(?), 73(?), 75(?), 74 
It is to be noted that the photographic method as here employed does 
not enable us to determine the critical potential of each line independently, 
as does the ionization method ; but only serves to classify lines if we assume 
they must all fall into three series, whose critical potentials are known. 
It is hoped to develop a method in which quantitative intensity measure- 
ments on the plate can be made. In this way curves similar to ionization- 
voltage curves can be obtained. 
This work has been carried out under the direct supervision of Prof. 
D. L. Webster, without whose very material aid it would have been 
impossible. 
1 Webster, D. L., and Clark, H., these Prockedings, 3, 1917 (181-5). 
2 Webster, D. L., Ibid., 6, 1920 (26). 
3 Webster, D. L., Ibid., 6, 1920 (269-72). 
4 Dershem, E., Physic. Rev., Ithaca, 11, 1918 (461-76). 
6 Overn, O. W., Ibid., 13, 1919 (137-42). 
6 de Broglie, M., C. R. Paris Acad. Sci., 169, 1919 (962-5). 
7 Siegbahn, M., Phil. Mag., London, 38, 1919 (639). 
