550 Sir William Crookes. [Jan. 26, 



This bright band may very well correspond to the a Cygni enhanced 

 iron lines 4549*64 and 4556*06 thrown together in the /x Centauri 

 spectrum. It is possible, though, that the dark line 4553 '4, quoted by 

 Pickering, is only the dark interspace between the bright 4549 '64 and 

 4556-06 lines. 



It may be here remarked that among the brightest lines in the 

 spectra of Novse at their initial stages are lines agreeing in position 

 with the most marked a Cygni and enhanced Fe lines, and in this way 

 we trace a resemblance between the minor bright lines of ju, Centauri 

 and the most conspicuous bright lines other than those of hydrogen 

 in the early spectra of Novse. 



Lines corresponding to these bright lines in n Centauri also occur in 

 the spectrum of y Cassiopeise, but they are far less well-defined in the 

 case of the latter star. 



The wave-lengths of the p Centauri lines given in the table were 

 reduced, by means of Hartmann's formula, from measures made on 

 Pickering's reproduction, the fiducial lines used being 4121'0 (He), H y , 

 and H/3. 



" On Europium and its Ultra-violet Spectrum." By Sir WILLIAM 

 CROOKES, D.Sc., F.R.S. Received January 26, Read February 

 9, 1905. 



Europium was discovered in 1901 by Dema^ay,* accompanying 

 samarium, from which he separated it by fractional crystallisation of 

 the double nitrates of magnesium and the earths. Demar^ay considered 

 that his new earth was identical with De Boisbaudran's Ze and Z, and 

 was the same which I had announced in 1885t as giving an extremely 

 sharp red line in the phosphorescent spectrum at wave-length 609 an 

 earth which in 1889J I said was a new one, and . designated by the 

 name of S6\ I detected the earth SS during an examination of the 

 phosphorescent spectra given by some of the fractions of samaria and 

 of yttria, neither of the earths being pure. 



Europium is the first member of the terbium group, gadolinium being 

 the second member. On the other side it comes next to samarium, the 

 last member of the cerium group. Assuming the oxide of europium 

 to be Eu 2 O3, the element has an atomic weight of 151 '8, from the 

 analysis of its sulphate, Eu 2 (SO 4 )3,8H20. 



* ' Comptes Kendus,' vol. 132, p. 1484, and ' Chemical News,' vol. 84, p. 1 



f ' Phil. Trans.,' vol. 176, p. 691. 



' Journ. Chem. Soc.,' vol. 55, pp. 250285. 



