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On Radiant Matter Spectroscopy. [Feb. 17, 



Respecting the theoretical considerations involved in these results, 

 I see two possible explanations of the facts brought forward. Ac- 

 cording to one hypothesis, research has somewhat enlarged the field 

 lying between the indications given by ordinary coarse chemistry 

 and the searching scrutiny of the prism. Our notions of a chemical 

 element have expanded. Hitherto the molecule has been regarded 

 as an aggregate of two or more atoms, and no account has been taken 

 of the architectural design on which these atoms have been joined. 

 We may consider that the structure of a chemical element is more 

 complicated than has hitherto been supposed. Between the molecules 

 we are accustomed to deal with in chemical reactions and the 

 ultimate atoms, come smaller molecules or aggregates of physical 

 atoms ; these sub-molecules differ one from the other, according to 

 the position they occupied in the yttrium edifice. 



An alternative theory commends itself to chemists, to the effect 

 that the various bodies discussed above are new chemical elements 

 differing from yttrium and samarium in basic powers and several 

 other chemical and physical properties, but not sufficiently to enable us 

 to effect any but a slight separation. One of these bodies, Gr£, gives 

 the phosphorescent citron line, and also the brilliant electric spectrum. 

 The other seven do not give electric spectra which can be recognised 

 in the presence of a small quantity of Gr5, whilst the electric spectrum 

 of Gd is so sensitive that it shines out in undiminished brilliancy 

 even when the quantity present is extremely minute. In the process 

 of fractionation, Ga, Gy3, Gc, &c, are spread out and more or less 

 separated from one another, yet the separation is imperfect at the 

 best, and at any part there is enough GS to reveal its presence by 

 the sensitive electric spark test. The arguments in favour of each 

 theory are strong and pretty evenly balanced. The compound mole- 

 cule explanation is a good working hypothesis, which 1 think may 

 account for the facts, while it does not postulate the rather heroic 

 alternative of calling into existence eight or nine new elements to 

 explain the phenomena. However, I submit it only as an hypothesis. 

 If further research shows the new element theory is more reasonable, 

 I shall be the first person to accept it. 



Neither of these theories agrees with that of M. Lecoq de Bois- 

 baudran, who also has worked on these earths for some time. He 

 considers that what I have called yttrium is a true element, giving 

 a characteristic spark spectrum, but not giving a phosphorescent 

 spectrum in vacuo. The bodies giving the phosphorescent spectra he 

 considers to be impurities in yttrium. These he says are two in 

 number, and he has provisionally named them Za and Z/3. By a 

 method of his own, differing from mine, M. de Boisbaudran obtains 

 fluorescent spectra of these bodies ; but their fluorescent bands are 

 extremely hazy and faint, rendering identification difficult. Some 



