272 Dr. Megh Nad Saha on the Problems of 



series-formula is composed. Tims, for the principal scries, 

 the series-formula is 



v=(l,s) — (m,p), m^2. 



When the atom is in a free gaseous condition, and is not 

 subject to any stimulus, it has the energy A— 7i(l, s). The 

 higher orbits are produced only when a stimulus is applied. 

 The lines are emitted as the electron chano-es its habitat 

 from one stable orbit to another with less energy. Thus 

 the line (l 9 s) — (2,p) is emitted when the electron changes 

 its habitat from the ^-orbit (2,p) to the s-orbit (1, 5), etc. 

 The law according to which these changes take place has 

 been thus formulated by Rubinowicz * and Bohr. Let n 

 and n denote the rotational quantum numbers of the initial 

 and final orbits. Then 



n — nQ=], 0, or — 1. 



We can thus distinguish among the following different 

 types of combination : — 



Group I. — Positive combination, n— -n =l. 



Combination "] (l,s)-(m,p) 1 (2,p)-(m,d) ~\ (3,d)-(m,f) 



m 



y'2 f ill y 3 V m > 4 



,1 



Accepted Appellation. J Principal Series. J Diffuse Series. J Bergmann Series. 1 

 (2,s)-(,n,p) (3,p)-(m,d) 



in 



\ 3. m y 4. etc. 



Group II. — Negative combination, n—n =— 1. 

 Combination ] (2,p)—(m,s) 1 (S,d) — (m,p) ~\ 



in 



>1. m> 2. 



Accepted Appellation. J Sharp Series. ) J etc. 



Group III. — Neutral combination. 



Combination (l,s)-(m,s) (2,p)-(m,p) (3,d)-(m,d) 



Each of the terms (m, s), (w,p), (m,d) may have double 

 or multiple values owing to the different possible orienta- 

 tions of the vibrating electron with regard to the remaining 

 atom f. 



* Kubinowicz, Phys. Zeits. vol. xix. pp. 441-465 (1918). Sommerfeld, 

 Atombdu unci Spektr airmail/ se, pp. 390-403. 



f For a theoretical treatment of the case, see S. N. Basu, " On the 

 Deduction of Rydberg's Law from the Quantum Theory of Spectral 

 Emission/' Phil. Mag. Nov. 1919. 



