﻿778 Dr. Marshall Watts on the Principal Series 



Other formulae which have been employed (besides that of 

 Kayser and Runge, which is not sufficient) are the Ritz 

 form 



O.F.=C.F. 109675 c „ 



and that of Lohuizen 



O.F.=C.F.- m675 



A comparison of the results given by these different formulae 

 is calculated to afford useful guidance in the examination of 

 less extended series. 



The case of Sodium has been examined at length by 

 Birge*, who gives wave-lengths on the Fabry and Perot 

 scale reduced to vacuum, and employs the Ritz formula 

 with 109678-6 as the value of N instead of 109675. 



In the table on pp. 776-7 I give the wave-lengths calculated 

 from the formula 



O.F.=41448-67- _ -i^ 7 !-^^ 



for the less refrangible component, and 



109675 



O.F. = 41448'67- 



m+ -148204 =- ) 



\ m — 1 / 



for the more refrangible component of the pairs of lines. 



In Potassium the formulae 



O.F. = 35005-56. 



C , oow* '061356\ 2 ' 



( m + '2930/6 ^- ) 



V m-1 ) 



r\ -n oK/^^r k- 109675 



O.F. = 35005-56- 



\ m — 1 J 



give the following values : — 



* Astrophys. Journ. xxxii. p. 112 (1910). 



