CHAPTERS IN SPECTRUM ANALYSIS. 



By W. MARSHALL WATTS, D.Sc. 



I. — Law and Order in Spectra. 



A. Line Spectra. 



(Continued from page 101.) 



In the spectrum of lithium, besides the principal 

 series, three other series have been observed. 

 Two of these — the " diffuse " (or first subordinate) 

 and the " sharp " (or second subordinate) series 

 have the same convergence-frequency at 28579-35. 

 The formula for the diffuse series is : — 



O.F. = 28579-35 - 



109675 



w+ i.ooii7-: 005}{8 ) 2 



m I 



and that for the sharp series is 

 O.F. = 28579-35 



109675 



m + -602191 - 



•013039\ 2 



in 



The Diffuse Series in Lithium. 



The Sharp Series in Lithium. 



Certain remarkable relationships between the 

 different series have been observed, which show 

 that they are not independent of each other. 

 If, for brevity, we denote the three series by 

 P, D, and S, and their convergence-frequencies 

 by Poo, Deo, and Soo, the first relationship is 

 that Doo = Soo. 



In the next place Poo - Soo gives the oscillation- 

 frequency (P 2 ) of the principal series. Thus in 

 lithium Poo =43482-52 

 Soo =28579-35 



P 2 =14903-17 



The following are the observed values of this line :— 



6708-0 Ramage, in flame. 



6708-2 Kayser and Runge, in arc. 



6708-10 Exner and Haschek, in arc. 



6708-2 Edcr and Valenta, in spark. 



6708-09 Exner and Haschek, in spark. 



This relationship was discovered independently by 

 Rydberg and by Schuster, and is generally called 

 the " Rydberg-Schuster Law." This law probably 

 holds good for all elements. It is interesting to 

 note that in 1896 Schuster predicted that a pair of 

 caesium lines, at about 8908 and 8518, would be 

 found in the infra-red — a prediction verified by 



the discovery of the pair j 0=97.70 by Lehmann in 



1901. A " diffuse " series and a "sharp" series exist 

 in the spectra of sodium, potassium, rubidium, and 

 caesium, each series consisting of pairs of lines, 

 as in the corresponding principal series. These 

 subordinate series have the pairs of lines always 

 at the same distance apart, as measured in 

 oscillation-frequency, whereas in the principal 

 series they get closer and closer together as they 

 approach the convergence-frequency. Further, 

 the constant difference in the two subordinate 

 series is exactly that of the first pair in the principal 

 series. This difference is 17-19 for sodium, 57-87 

 for potassium, 237-98 for rubidium, and 553-96 

 for caesium, these numbers being approximately 

 as the squares of the atomic weights of the corre- 

 sponding elements. 



In sodium the common convergence-frequency of 

 the diffuse and sharp series is 24475-89 for the less 

 refrangible lines, and 24475-89+17-19=24493-08 

 for the more refrangible lines. If we subtract 

 these numbers from 41448-67, the convergence- 

 frequency of the principal series, we get 16972 - 78 

 and 16955-59 as the oscillation-frequencies of the 

 two P„ lines, and these correspond to the wave- 

 lengths" 5890-19 and 5896-16 respectively. The 

 observed values of these lines are : 



5806-16 K avser an d Runge, in the arc. 



58Q6-T4 Rowland, in the sun. 



which corresponds to the wave-length 6708-16. 



5890-18) 

 5896- 15J 



5896 -?7 1 E xner an< ^ Haschek, in the arc. 



5890-21 



5896 



Eder and Valenta, in the arc. 



.91 -\ 

 To} Exner and Haschek, in the spark. 



U8 



