﻿1138 Prof. M. N. Saha on Temperature Ionization of 



only as a neutral and a singly-ionized atom, but also at least 

 as a doubly-ionized element, and the stages follow each other 

 in rather quick succession. 



Titanium. — The spectrum of Ti is very well studied, though 

 the series classification is not yet known. In their general 

 behaviour the lines of Ti, Ti + , and Ti ++ resemble the corre- 

 sponding lines of Si, Si + , Si + + , but titanium becomes 

 ionized at a much earlier stage than Si, which is in ac- 

 cordance with the general rule that for elements belonging 

 to the same group, heavier elements have got the smaller 

 I.P. Lines of Ti+ (\ = 3759'47, 3761*47, 4578*19) are 

 quite strong in the solar spectrum, and according to W. J. 

 S. Lockyer *, they are more intense in F5G stars ((/> Cassio- 

 poeice) than in A2F stars (a Cygni). The ionization of Ti 

 commences much earlier than that of Si. 



Group V. Nitrogen, Phosphorus, Vanadium. 



The enhanced lines in the spectrum of Nitrogen and their 

 occurrence in stellar spectra were first noted by Lockyer, 

 Baxandall, and Butler |. The subject has been subsequently 

 treated by Lunt, Fowler, and Wright. 



According to these workers, the spectral lines of nitrogen 

 can be divided into 2 or 3 groups according to the 

 stimulus necessary for exciting them. The chief lines of 

 Group I. are \ = 3995*15, 4147'20, 463073, and the chief 

 lines of Group II. are X = 409748, 410354, 464082, 

 4634*34. There is, besides, another line at 4379'26 which 

 seems to belong to an enhanced group of still more pro- 

 nounced type. Since lines of Group I. do not occur in the 

 low-temperature spectral classes like G, F, and even at Ao J, 

 I am inclined to think that they are due to N + , or belong to 

 some remote combination of the neutral nitrogen series In 

 the former case, Group II. would correspond to N ++ . They 

 first come out in the B2 classes (intensity 1), and gradually 

 increase in intensity as we go to the still hotter stars, as the 

 following shows : — 



29 Canis Can. Mai. e Orionis „ . r\ • ■ 



t, t . ■ /r \ \ /r\ ~\ /m\ P Centauri. y Ononis. 



N+ + (4097-45)... 18 6 4 2 1 



* W. J. S. Lockyer, loc. cit. 



t Lockyer and others, Proc. Roy. Soc. Lond. A. vol. clxxxii. p. 532. 

 Lun,t, Monthly Notices, lxxx. p. 534 (1920). Fowler, Monthly Notices,, 

 lxxx. p. 693. 



J Of this last I am not quite sure. 



