570 



REPORT 1886. 



and baffling tongue. All attempts to deciplier the mysterious signs were, however,, 

 for a long time fruitless. I required a Rosetta stone. 



Down to a date comparatively recent nothing was more firmly fixed in my mind 

 than the notion that yttria was the oxide of a simple body, and that its phosphores- 

 cent spectrum gave a definite system of coloured bands, such as you see in the 

 drawing before you (fig. 2). Broadly speaking, there is a deep red band, a red 

 band, a very luminous citron-coloured band, a pair of greenish-blue bands, and a 

 blue band. It is true these bands varied slightly in relative intensities and in 

 sharpness with almost every sample of yttria I examined ; but the general cha- 

 racter of the spectriim remained unchanged, and 1 had got into the way of 

 looking upon this spectrum as characteristic of yttria : all the bands being visible 

 when the earth was present in quantity, whilst only the strongest band of all — the 

 citron tjand — was visible when traces, such as millionths, were present. But that 

 the whole system of bands spelled yttria, and nothing but yttria, I was firmly 

 convinced. 



During the later fractionations of the yttria earths, and the continued observa- 

 tions of their spectra, certain suspicions which had troubled me for some time 



?40 260 „ 280 „„ 300 „ 320 ._ 340 _ 360 __ 380 400 _ 420 



3 I 70 I 9,0 I 10 I 





H-:,' 



i*'-,;-^" 



^V-tfyii 



m 



-Fi^.2 Yttria 



iiiliiiiiii 



Vvyt -•-•»> -^-i 



Fief 5. la (Gaddinia) 



uL] 1 1 1 1 1 1 1 1 i 1 1 



J-LlLu I I I I I I I Li 1 I I I I I I I I n I I I I I I I I I I I I I I I I I I I I I I I I 1 I lli-LLLlXLI-LLLL 



If I 



Flci.4. Yttria.6J Scmtaria,59 



assumed consistent form. The bands which hitherto I had thought belonged tc 

 yttria began to vary in intensity among themselves, and continued fractionation 

 increased the dift'erences first observed. Whilst I was in this .state of doubt and 

 uncertainty, and only beginning to see my way towards arranging into a consis- 

 tent whole the facts daily coming to light, help came from an unexpected quarter. 

 M. de Marignac, wdth whom I had been for some time in correspondence, kindly 

 sent me a small .specimen of the earth which he had discovered and provisionally 

 named Ya (now Gadolinia). In the radiant-matter tube this earth gave a bright 

 spectrum, like the one in the diagram before you (fig. 3). The spectrum above it 

 (fig. 2) is that ascribed to yttria. Look at the two. Omitting minor detaDs, Ya 

 is yttria with the chief characteristic band — the citron band — left out, and with 

 the double green band of samaria added to it. Now look at fig. 4, which represents 

 the .spectrum of a mixture of sixty-one parts of yttria and thirty-nine parts of 

 samaria. It is identical almost to its minutest detail with the spectrum of Y''a^ 



