PHYSICS: WEBSTER AND CLARK 
181 
A more extended account of the investigation will be published in 
the near future. 
1 Barnett, S. J., Physic. Rev., Ithaca, N. Y., (Ser. 2), 6, 1915, (239-270). 
2 Einstein, A., and de Haas, W. J., Berlin, Verh. D. Physik. Ges., 17, 1915, (152-170, 
203, 420). 
3deHaas, W. J., Amsterdam, Proc. Sci. K. Akad. Wet., 18, 1916, (1281-1299); Sci. 
Abs., London, A., 17, 1916, (351). 
THE INTENSITIES OF X-RAYS OF THE L SERIES 
By David L. Webster and Harry Clark 
JEFFERSON PHYSICAL LABORATORY. HARVARD UNIVERSITY 
Communicated by E. H. Hall, January 17, 1917 
The purpose of this paper is to report briefly some preliminary re- 
sults of a study of the intensities of X-rays belonging to the L series of 
platinum considered as functions of the potential producing them and 
in their relations to each other and to the general radiation. 
Review of Previous Work. — Many of the phenomena observed here 
can be predicted, though with no certainty, by analogy with corre- 
sponding phenomena of the K series. The similarity of the two series 
appears in Moseley's laws^ of frequency as a function of atomic number, 
and especially in the fact that each series is produced as fluorescence by 
a substance absorbing rays of a higher frequency. It has been found 
by one of us^ that the K series rays, of rhodium at least, appear only at 
a potential high enough to produce general radiation of a frequency as 
great as that of the shortest line of the series. This may be called the 
critical potential. Since this result is obviously connected with the 
law that absorbed rays will produce the K fluorescence only if their 
frequency is above that of this line, it is reasonable to expect a similar 
law for the L series. 
It must be remembered, however, that the L series is more complex 
than the K, both in the number of lines and in their gradual shifting 
relative to each other from element to element, shown in Moseley's 
graphs^ of square root of frequency against atomic number of the emit- 
ting element. Moreover KosseP has found reason to believe that 
platinum and gold each show two discontinuities of absorptive power 
as a function of frequency near the L series, one in the middle of the 
series and the other near the high frequency end. An explanation of 
this appears in a most exhaustive study of the positions of the L series 
lines of the heavy elements by Siegbahn and Friman^ who have plotted 
l^p against N for twelve lines. Four of these graphs are linear and 
nearly parallel, while the eight others are not linear but are nearly 
