478 



Messrs. Runoe and Precht on the Position 



on the scale o£ frequency. The same holds good for radium, 

 as shown by the following table : — 





X. 10V^. Difference. 



Primary Series \ 



1st secondary Series \ 

 2nd „ „ | 



4682-35 21356-8 

 3814-59 262151 



1 

 4436-45 225405 

 3649-77 27399-0 



5813-9 ' 17200-2 

 4533-33 22058-8 



4858-3 

 4858-5 

 4858-6 



The variations in the numbers corresponding to the dis- 

 tances are sufficiently explained by experimental errors. 

 They correspond to very small errors in the wave-length 

 determinations. 



From one element to another the distance apart of the 

 lines increases with the atomic weight in the cases of Mg, 

 Ca, Sr, Ba :— 





Atomic weight. 



Distance. 



Mg... 



24-36 



91-7 



Ca ... 



40-1 



223 



Sr ... 



87-6 



801 



Ba ... 



137-4 



1691 



It is suggested to regard the atomic weight as a function 

 of the distance between the lines, and to extrapolate this 

 function for radium. It has already been pointed out by 

 Rydberg, Kayser and Runge, in their investigations on the 

 spectra of the elements, that within a group of chemically 

 related elements the distance apart of the lines of a pair 

 increases regularly with the atomic weight. They state that 

 iu the case of alkali metals the atomic weight is very nearly 

 proportional to the square root of this distance. We wish to 

 draw attention to the fact that for the other groups in which 

 line-pairs have been observed, the relation between the width 

 of the line-pairs and the atomic weight is capable of being 

 expressed by a simple formula : — 



In each group of chemically related elements the atomic 

 weight varies as some power of the distance apart of the two 

 lines of a pair. 



