PHYSICS: WEBSTER AND CLARK 
185 
wave lengths are used as standards. Whatever constant errors there 
may be in this determination of h will cancel out in the calculation of 
the critical wave lengths. 
TABLE I 
Line X h (erg sec) 
ai 1.313 A 6.59X10-27 
/?4 1.142 6.53 
1.120 6.54 
/32 1.101 6.53 
71 0.958 6.48 
Mean 6 . 53 
The intensities of the lines alone may be obtained by subtracting 
from the ordinates of their graphs the general radiation estimated as in 
figure 1. By this process it appears, as expected, that lines of the 
same series maintain the same ratio of intensities through any increase 
of potential up to 20 kv., the limit of our experiments to date. For 
potentials over 20% above the critical points, the mean deviation of 
these ratios from their average values is less than 3%. More accurate 
results should be obtained at higher potentials and with more exact 
determinations of the general radiation. The graphs both of lines and 
general radiation are also of the general forms predicted. Present 
results indicate that the rhodium K series and platinum Li and L2 
series all increase in intensity approximately in proportion to the three- 
halves power of the difference between the potential applied to the 
tube and the critical potential of the series. On all these points, how- 
ever, the present statements are only preliminary, and more accurate 
results should be obtained from further work now being done on plat- 
inum. Since the relation between the two series is different in different 
elements, we hope to test these phenomena in thorium also. 
iPM. Mag., London, (Ser. 6), 26, 1913, (1024-34); 27, 1914, (703-14). 
2 These Proceedings, 2, 1916, (90-4); Physic. Rev., Ithaca, N. Y., (Ser. 2), 7, 1916, 
(599-613). 
^Berlin, Verh. D. Physik. Ges., 16, 1914, (898-909). 
^Phil. Mag., London, (Ser. 6), 32, 1916, (39-50). 
^Ibid., 32, 1916, (497-499). 
Ubid., 26, 1913, (210-232), see especially p. 225. 
'The instrument was made from our design by the Alvan Clark Corp., Cambridge, 
Mass. 
