638 



Dr. S. R. Milner on the 



Their wave-lengths were measured on the calcite spectro- 

 graph. With four hours' exposure the series down to ra = 16 

 was well developed, traces of several further lines may be 

 seen, and on some of the negatives a faint indication of what 

 may possibly be the limit. There is a slight diminution in 

 density just beyond the point where the limit should 

 theoretically be, but it is too faint to speak with certainty 

 of it. 



Principal Series, 



m. 



\ (air). 



n (vac). 



5 



J 5354 3 

 1 5316-0 



18671-5 



18806-0 



6 



/ 512093 

 1 5102-85 



195224 

 19591-5 



7 



J 4981-28 



20069-7 



8 



/ 4890-0 



\ 4884-0 



20444-3 

 20469-4 



9 



4826-36 



207139 



10 



4781-07 



20910-1 



11 



474772 



21057-0 



12 



4722-09 



211712 



13 



4701-96 



21261-9 



14 



4684-86 



21339 5 



15 



4672-38 



21396-5 



16 



4661-29 



21447-4 



The principal series should theoretically consist of triplets 

 converging to a common limit; the higher lines are all very 

 diffuse, they show distinct evidence of broadening from 

 m = 12 to m = 9, m = 8, 6, 5 are double, m = 7 is possibly 

 double also, as the smaller wave-length component may be 

 swamped by the spreading out of the over-exposed strong 

 line X 4959*7 close to it. X 5354 (m = 5) shows a considerable 

 broadening towards the red, which may be due to the partial 

 separation of a third line of the triplet ; on the other hand, 

 Kayser and Runge give a faint nebulous line 5365*25 which 

 may be the cause of it. Beyond this point it is difficult to 

 identify the series lines. Paschen from his observations in 



