PEOF. W. M. HICKS: A CKITICAL STUDY OF SPECTEAL SEEIES. 



63 



raises a suspicion that the rise exists and that v is not constant. It is just possible, 

 as we shall see later, that the sodium series, which has generally been taken as the 

 typical diffuse, may not be so. 



As regards (B), the following table gives the values of v for the alkalies, as 

 determined by least squares (duly weighted) for Na and K and arithmetical means 

 for Rb and Cs from the observations of K.R., SAUNDERS, and RAMAGE : 



Any doubt, however, as to the exact truth of (A) and (B) must vanish when we 

 consider those elements in which v is very large. As examples, take Tl for doublets 

 and Hg for triplets. In the case of Tl we find the following values of v : 



Sharp. 



7792-37 ( -31) 

 7792-63 ( -73) 

 7792-46 (1-18) 

 7790-92 (275) 

 7789-22 (7-22) 

 Most probable v = 7792'39. 



Diffuse. 



7793-08 ( -63) 

 7792-64 ( -87) 

 7791-69 (2-40) 

 7791-68 (6-82) 

 7790-22 (8-14) 

 Most probable v = 7792'90. 



Most probable supposing both same = 7792-51. 



The corresponding values for Hg are : 



Sharp. 

 i>i 468178 



v a 1767-59 



Diffuse. 

 4631-79 

 1768-52 



If there were real variations, we cannot but believe that they would bear some 

 relation to the absolute magnitude of v. Yet here, even with such exceedingly large 

 values of v, the variations do not exceed the corresponding values for small v. We 

 need, therefore, feel no hesitation in imposing the laws (A) and (B) as conditions 

 which our formula must fulfil. 



As to (C) there cannot be quite the same degree of certainty. The principal series 

 have only been observed in the alkali metals and He among doublets and O and S 

 amongst the triplets. In the alkali metals v for NaP (1) is known with extreme 

 accuracy, viz., v = 17 '21 (from interferential measurements). For the others the 

 measurements are very bad. For K, KAYSER and RUNGE give 5 7 '08 (very large 

 possible errors), SAUNDERS 57 '8 7, and LEHMANN 56 "43. For Rb, SAUNDERS gives 

 237'73, LEHMANN 232'76. For Cs, LEHMANN gives 553-00. In every case (C) is 



