12 



THE ROYAL SOCIETY OF CANADA 



III. Series Spectra 



An attempt was first made to select wavelengths which might 

 possibly belong to the series n = (1 • 5,S) — (m,P) by using the strongly 

 absorbed wavelength A = 2170 A°U in combination with the wave- 

 lengths given respectively by the resonance potential 1-26 volts, and 

 the ionisation potential 7-93 volts. It was not found possible to 

 select a series of wavelengths which would fit exactly to a simple 

 formula, but the following grouping appeared to merit some consider- 

 ation : 



Table II 



Principal Series 



n = (1-5, S) - (m. P) 

 (1-5, S) = 64311 



The third and fourth numbers of this series were calculated by 

 applying the method of Savidge and Nicholson,^ and using the wave- 

 lengths of the first two members of the series as given in the table as a 

 basis. A graph. Fig. 2, was drawn showing the values of V'[N/(A— n)] 

 for the series plotted against successive integers. The fact that it is 

 regular and nearly linear shows that the series fits in fairly well with 

 a formula of the Ritz-Rydberg type. This is especially interesting 

 when it is considered that the first wavelength lies in the infra-red 

 region and the second well down in the ultra-violet. 



The wavelengths in this series all appear with strong intensity 

 in the spark emission spectrum of lead^ in air, but it will be noted 

 that the only one shown to be absorbed by non-luminous lead vapour 

 isA=2170-5A°U. 



Assuming the above wavelengths to accurately represent the 

 principal series n = (1 • 5,S) — (m,P) one can readily calculate the wave- 

 lengths of corresponding sharp subordinate and diffuse subordinate 

 series. This has been done and the wave lengths are given in Table 

 III and Table IV. 



'Savidge and Nicholson. Phil. Mag. p. 563, 1915. 



2 McLennan, Ainslie and Fuller. Proc. Royal Soc, A. 95, p. 316, 1919. 



