1887.] on Genesis of the Elements. 47 



I now will introduce to yon a substance which has been to me 

 what the celebrated Rosetta stone was to the interpreters of Egyptian 

 inscriptions. I received it from M. de Marignac, and it was nothing 

 more than a small specimen of a new earth which he had obtained 

 and had named provisionally Ya. 



In the radiant-matter tube this earth gives a bright spectrum as 

 in the diagram before you (Fig. 3). 



If we compare this spectrum with that ascribed to " old yttrium " 

 (Fig. 2) we see that, omitting minor details, Ya is yttrium with the 

 characteristic citron band left out and the green and orange bands 

 of samarium added. Now look at the following diagram (Fig. 4), 

 which represents the spectrum of a mixture of 61 parts of yttrium and 

 39 parts of samarium. It is almost to its minutest details identical 

 with the spectrum of Ya, but the citron band is as prominent as any 

 other band. Hence Ya is shown to consist of samarium, with the 

 greenish blue of yttrium and some of the other yttrium bands added 

 to it. It proves, further, that the citron band which I had hitherto 

 regarded as one of the essential bands of the yttrium spectrum can be 

 entirely removed, whilst another characteristic yttrium group, the 

 double green band, can remain with heightened brilliancy. 



If now it were possible to remove the citron band-forming body 

 from this mixture, I should leave Ya behind ; I should, in fact, have 

 recomposed Ya from its elements. "I have no doubt whatever that 

 this will ultimately be accomplished, but the preliminary work of 

 fractionation is tedious to the last degree, and for its completion 

 would occupy a space of time in comi^arison with which the life of 

 man is all too brief. 



Whilst I have not yet chemically removed the citron -forming con- 

 stituent, I can physically suppress the citron band and show an 

 artificial spectrum, imitating in the closest degree the natural si)ectrum 

 of Ya. 



By means of the electrical phosphoroscope I am enabled to catch 

 the spectrum of an earth immediately after it has suffered molecular 

 bombardment in the vacuum. In this way I get the spectrum of the 

 residual phosphorescence, and I have found that not all the con- 

 stituents of these earths emit residual phosphorescence for the same 

 duration of time. 



When a little strontium is added to the yttrium-samarium mixture, 

 the effect in the phosphoroscope is to suppress the residual phosj^hor- 



fluorescent bands are extremely hazy and faint, rendering identification difficult. 

 Some of tliem fall near lines in the spectra of my G)8 and G5. At first sight it 

 miglit appear that his and my spectra were due to the same bodies, but, 

 according to M. de Boisbaudran, the chemical properties of the earths producing 

 them are widely distinct. Those giving phosphorescent lines by my metliod 

 occur at tlie yttrium extremity of the fractionation, where his fluorescent bands 

 are scarcely shown at all ; whilst his fluorescent phenomena are at their maximum 

 quite at the terbium end of the fractionation, where no yttrium can he detected 

 even by the direct spark, and where my phosphorescent lines are almost absent. 



