and the Theory of Atomic Structure. 1103 



Ku 1 and K« 2 lines though very faint were in second order 

 observed on the plate. From a thorough examination of 

 the plates, however, we are inclined to conclude that the 

 line 74 does not exist for Od or at any rate must be still 

 weaker than in the case of In. For the next element (Ag) 

 we are troubled by the increased absorption in the photographic 

 plate (L 3 discontinuity), so that for this element nothing can 

 be stated about the existence of <y 4 . A complication showed in 

 the photographs of the Pd (46) and Rh (45) spectra. Besides 

 a very faint iine at 3450 X.U. for Pd and at 3651 X.U. for 

 Rh, which might be considered to be y^ another line of the 

 same appearance was found for both elements. (For Pd 

 \ = 3433 and for Rh \ = 3631.) These lines, however, have 

 shorter wave-lengths than the extrapolated values of the 

 respective L 3 discontinuities. 



§ 6. The lines /3 2 and <yj depend on the existence of the 4 3 

 electrons in the N-shell, which electrons according to Bohr 

 are found for the first time in the neutral atom of Y (39). 

 Relatively to the other lines of the L-spectrum /3 2 and 7l 

 have their ordinary intensity as far down as Mo. For Nb 

 however they are considerably weaker compared with the 

 other lines, for Zr they are both very faint. For Y, /3 2 and y ± 

 were not visible, but here the plates were not especially good. 

 For Sr and Rb, for which the plates were quite good, <y x had 

 wholly disappeared. If we extrapolate /3 2 according to 

 Moseley's law, this line almost coincides with /3 4 in the case 

 of Sr, while for Rb it should lie on the long- wave- length 

 side of /3 4 . A faint line was actually found in this place. 

 On different plates, however (taken with different Rb salty), 

 the relative intensity of this line seemed to show considerable 

 variations. This could easily be understood if the line were 

 due to some other element. Thus it seems to be most 

 probable that /3 2 disappears at the same time as y 1 between 

 Zr(40) and Sr(38). The lines M 7 and MS should dis- 

 appear at the same time as L/3 2 find L^. As these lines 

 must have a wave-length of about 37 A.U. for Nb, 

 they cannot be studied in this region in the present state of 

 spectroscopy. 



§ 7. As for the line L/3 7 it was not possible to identify it 

 in the region under consideration. This line is also for the 

 heaviest elements a rather faint line. For Pt and the 

 elements with higher atomic number it seems to be a double 

 line. This is difficult to explain in the light of our present 

 knowledge of the X-ray spectrum. As has also been observed 

 by Dauvillier, it is a single line for W, and I was able to 



