212 ANNUAL REPORT SMITHSONIAN INSTITUTION, 1925 



mined that in certain of your fractional solutions of didymiuni, cer- 

 tain bands in the blue region — particularly the group of bands, 

 A=:449 to 443 — had a special importance, equaling in intensity the 

 group in the yellow — A:^590 to 5G8. At first you attributed them 

 to lanthanum, but later knew that this element took no part in the 

 ])lienomonon. Now it is certain that the blue band belongs to pra- 

 seodymium and the 3'ellow to neodymium. Thus, von Welsbach, to 

 whom the discovery is generally attributed, was really later than 

 you in the separation of these two elements. I am not surprised 

 that the honor of the discovery was attributed to him, for in such 

 matters the scientific world is indifferent and allows itself to be 

 misled by appearances. 



One would be very incompetent to wrongly estimate the results 

 of your researches. We forget too often that in order to judge the 

 value of a discovery it is necessary to consider the conditions under 

 which it was made and make proper allowance for the progress 

 science has made since. Within our times ideas have developed 

 rapidly, and experimental technique has been improved with incon- 

 ceivable rapidity. The two processes have been mutually helpful. 



The 25 years I have spent in the study of the rare earths give 

 me the right to affirm that it would have been impossible in 1880 

 to have pushed farther than you did the researches on the separa- 

 tion of did_ymium. Didymium was very rare, the methods of frac- 

 tionization ver}^ rudimentary, i)reventing you from carrying the 

 separation very far; but that should mean more credit for obtaining 

 the results then, than for i)erfecting them later. 



Those early days were days of misery in the study of the rare 

 earths — I have known in comparison only days of relative opulence, 

 and I salute 3^ou, my dear Brauner, one of the pioneers whose work 

 has always filled me with admiration and profound respect. 



Somewhat later there occurred in the domain of the rare earths 

 a very orgy of spectrum variation. Your immediate successors seem 

 to have endeavored by their excesses to discredit the work of their 

 predecessors. The spectrum bands seemed to lose all orderliness. 

 Your neodymium and praseodymium, the samai-ium and the 

 dysprosium of Lecoq de Boisbaudran, the holmium of Soret and 

 Marignac (and not of Cleve, to whom it is often attributed), the 

 erbium of Mosander, and the thulium of Cleve, in short iill the ele- 

 ments of the absorbent-spectra group, seemed to multiply ad infini- 

 tum. Kriiss and Nilson, H. Becquerel, Crookes, and all the 

 world with them, noted the variations in the intensity of the differ- 

 ent absorption bands in ever-changing proportions. Each one 

 wished to discover and believe he had seen a new element. Such 



