CHEMICAL ELEMENTS AND ATOMS — URBAIN 201 



active members and mIio inaugurated the era of high precision in 

 the determination of atomic Aveights. 



Your work upon atomic weights is universally appreciated and 

 probably better known than that upon the rare earths. Its ob- 

 jective is broader. Your merit and high scientific acumen came 

 into relief Avith the publication of your admirable study of atomic 

 weights found at the beginning of Abegg's Encyclopedia of Physi- 

 cal Chemistry. What striking honor this was to a Czech scientist. 



The International Union of Pure and Applied Chemistry bore 

 in mind this work at the very outset when they came to naming 

 the members of the Commission on Chemical Elements and later 

 when choosing the president of the subcommittee on atomic weights. 

 I recall that Guye, whose ideas upon atomic weights did not wholly 

 agree with yours, insisted that the presidency be given to you. 

 Such acts of courtesy in all impartiality on the part of opponents 

 show the value of a man. The two incidents just recalled show 

 how universally you are recognized as the master in the domain 

 of atomic weights. 



An especiall}'^ important task devolves upon the president of the 

 commission. He drafts the report and prepares the table of inter- 

 national atomic weights. He must know the relations existing be- 

 tween the diverse atomic weights and judge their relative impor- 

 tance. He must be able to appreciate the relative worth of the 

 values determined by various men. To bring such a delicate task 

 to a proper conclusion requires good scientific judgment, a judicious, 

 critical spirit, and an impartiality overlooking the rivalry of differ- 

 ing schools. 



Now, shall we recall briefly our common recollections of the won- 

 derful journey which we have made through contemporary scientific 

 history, more especially through the domain of the chemical ele- 

 ments ? In an epocli when time is no longer considered as immutable, 

 we have surely lived existences which, measured by the importance 

 and number of events which we have seen unroll before our eyes, 

 have been the equivalent of several generations- Judging by you 

 (Brauner) the limit of the youth of the spirit has been greatly ex- 

 tended. Scientific evolution has been a part of the change. Our 

 times are privileged. They have seen many important problems pro- 

 posed, a number of which have had surprising solutions. We have 

 traversed the enormous distance which separates the elements of 

 Lavoisier and of Berzilius from the isotopic constellations of Aston. 

 AVith Bunsen you saw the birth of the first spectroscopic elements 

 in the flame. You have contributed to the genesis of those elements 

 recognized through their absorption spectra, for you were the first 

 to see the element called praseodymium. A collective error, which 



