274 JOURNAL OF THE WASHINGTON ACADEMY OF SCIENCES VOL. 11, NO. 12 



manner potentials have been found which are determined by the 

 limiting frequency of the softest X-ray series of a number of elements. 

 Table 1 gives the observed potentials, and the corresponding wave 

 lengths for these X-rays. Carbon was studied in the compounds 

 CO, COo, C2H4 and CCI4. The latter compound also gave the chlorine 

 points. The nitrogen point was obtained from air and the other 

 points from the various elements at temperatures giving suitable 

 vapor pressures. 



The limits La of the L series for light elements, computed from X-ray 

 spectral data by the relation La = Ka- K^, are included in table 1. 

 A plot of V Vx against atomic number shows that both the observed 

 (column a) and computed points from magnesium to chlorine fall on 

 the same straight line within the probable observational error. The 

 points h for these elements lie on a nearly parallel line. They indicate 

 a new X-ray series of feeble intensity. The value of L^ for sodium 

 falls above the extrapolated straight line but is consistent with Milli- 

 kan's recent observation of the L„ lines as X = 372 and 376A. The K 

 limits found for carbon and nitrogen fall close to the extrapolated Ka 

 line. The carbon point is in fair agreement with the value X = 42.6 A 

 found by Kurth- who observed the radiation from a solid carbon 

 anode. Theories of atomic structure indicate that the potassium 

 points must be related to the M series. 



The above preliminary results emphasize the value of this method 

 of stud^dng radiations in the region between the range of the vacuum 

 spectroscope and the X-ray crystal spectrometer. 



2 Abstract in Phys. Rev. 17: 528. 1921. 



