548 Sir N. Lockyer and Mr. F. E. Baxandall. [Jan. 4, 



" Note on the Spectrum of p Centauri." By Sir NORMAN 

 LOCKYER, K.C.B., LL.D., Sc.D., F.E.S., and F. E. BAXANDALL, 

 A.K.C.SC. Keceived January 4, Read February 9, 1905. 



An investigation of Pickering's reproduction of this spectrum* 

 which apparently consists of the spectrum of an Orion star + bright 

 hydrogen lines and certain other bright lines of minor intensity 

 suggested that the latter are radiation lines corresponding to some of 

 the stronger absorption lines of a Cygni. These a Cygni lines have 

 previously been attributed to the enhanced lines of certain metals, 

 chiefly Fe, Ti, Cr, Mg, and Si. 



A close investigation has now shown that nearly all the most marked 

 bright lines in //. Centauri other than those of hydrogen occupy 

 positions closely corresponding to those of the most conspicuous 

 enhanced lines of iron. The wave-lengths of some of the bright 

 u Centauri lines are compared with those of the enhanced lines of iron 

 and a Cygni lines in the table at the end of this note. The close 

 agreement is very noticeable. 



It is worth while, then, to analyse in detail Pickering's statement in 

 his notef on the p Centauri spectrum. He states : "Lines 4922'! and 

 5015*8 are bright on the edge of greater wave-length." The lines 

 whose wave-lengths he gives are the helium-Orion absorption lines. 

 The only two enhanced iron lines in this region are at XX 4924*11 and 

 5018*63, which occupy exactly the positions relatively to the helium 

 lines which Pickering notes as being bright in the p Centauri spectrum 

 that is, they border the helium lines on the edge of greater wave- 

 length. 



Again, he says : " The two most conspicuous (bright lines) are at 

 wave-lengths 4232 and 4584 approximately," Two of the most marked 

 lines in the a Cygni spectrum are at XX 4233*25 and 4584*02, and 

 these undoubtedly correspond to the two most conspicuous enhanced 

 lines of iron between H and H/s. 



Again. " Line 4387*8 is bright on the edge of shorter wave-length. " 

 In a Cygni there is a well-marked line at X 4385*55, which agrees in 

 position with another enhanced iron line. 



Also : " A diffuse bright band appears on the side of shorter wave- 

 length of the dark line 4531 *4." There is a distinctive group of a Cygni 

 enhanced iron lines at XX 4508*46, 4515*51, 4520*40, 4522*69, which, 

 thrown together into an irresolvable group in ^ Centauri, may well 

 correspond to the diffuse line quoted by Pickering. 



Further: " The dark line 4553*4 is superposed on a bright band." 



* 'Annals Harv. Coll. Obs.,' vol. 28, Part II, Plate 1. 

 f ' Annals Harv. Coll. Obs.,' vol. 28, Part II, p. 178. 



