OS 



KNOWLEDGE. 



April, 1915. 



For rubidium the formulae 

 OF. = 33688-20 - 



Kl«Mi75 



(l.r. 



O.F. = 33688-20 - 



(„+.; ,,•_,;,.„ _±Z3542y line) 

 V m — \ 



109675 



•l)738()»\" ,: 



, ( m - r - 



( m + . 365934- '""""'"I Hno 

 \ wi — 1 / 



give equally p""l results, as shown in the following 

 tabic: 



Table 19. 

 The Principai Series in Rubidium. 



In caesium the formulae 



O.F. = 31404-6 



109675 



O.F. = 31404-6 - 



m + -418206- 

 109675 



•09002 \ a 



m — 1 



( m + . 449975 _l089294y 

 \ m — 1 / 



give the following results : 



Table 20. 

 Tin: Tkincipal Series in Caesium. 



The remarkable similarity between the spectra 

 of the alkali metals was noticed by the early 

 observers. In 1869 Lecoq de Boisbaudran remarks 

 that the spectrum of caesium is, like that of 

 potassium, shifted bodily towards the red. Figure 

 78 is a photographic reproduction of some of the 

 beautiful drawings of spectra published by de 

 Boisbaudran. The caesium and rubidium lines 

 which he marks a, 6 are those of the principal series 

 marked m=3 in Figure 79 (the diagram does not 

 extend far enough to the right to allow of the red 

 lines of the three elements to be shown, i.e., those 

 for which m=2). 



That there exists some relationship between the 

 atomic weights of allied elements and their spectra 

 is certain. If we knew the precise law of this 

 relationship, the measurement of the wave-lengths 

 of the lines in the spectrum of a new or rare ele- 

 ment, particularly of one difficult to obtain in a 



