RADIOACTIVITY." 



By Prof. Dr. Franz IIimstedt, 

 Frorcctor of the University of Frclh>tnj in Brcis(/(ui. Baden. Clvrmany. 



In December, 1895, Rontgen made his first communication regard- 

 ing the X-rays to the physical medical society in Wiirzburg, and early 

 in 1896 Becquerel submitted to the Academy in Paris a treatise in 

 which it was authoritatively announced that he also had discovered 

 a species of rays not less wonderful, namely, those emitted by the 

 radioactive substances. 



A decade only has passed since then, but a decade so fruitful in the 

 discovery of new facts, so radically revolutionizing opinions and 

 views maintained for a century and apparently unassailable, and so 

 suddenh^ lighting uj) for us regions hitherto shrouded in deepest 

 obscurity, that another like it can hardly be pointed out in the history 

 of physics. And since it is incumbent on me to-day, after the old 

 academic custom, to enter upon the office of prorector with a short 

 address relating to my special department of research, I feel that I 

 can choose no more fitting theme than radioactivity. I believe that 

 not only the recent phenomena in this field, but also the attempts at 

 their explanation and a statement of the ncAv views which now obtain 

 regarding the constitution of matter, will prove such as to arouse 

 interest far be3''ond the circle of those concerned mainly with physical 

 science. 



In his first treatise on the X-rays, Rontgen drew attention to the 

 fact that they proceeded from those parts of the Rontgen tubes 

 where the glass, imder the influence of the impinging cathode rays, 

 showed the most fluorescence. It therefore seemed possible that the 

 existence of these mysterious rays was in some way dependent on 

 jDreviously acquired fluorescence, and many physicists tried to ascer- 



" Traushited. by lu'i'iiiissioii. I'roni Kedeu, gehalten in der Kunst-iind Festhalle 

 am IC) INIai ll>0(j bei der offentlieben Feier der tJbergabe des I'rorektorats der 

 Universitiit Freibiu'g i. Br. vou dem abtretendeu I'rorektor Prof. Dr. Tbeodor 

 Axenfeld imd dem antretenden Prorektor Geh. Hofrat Prof. Dr. Franz Himstedt, 

 Freiburg i. Br. UuiversitUts-Bucbdruckerei U. Hochreutber, 1000, pp. 31-G.3. 



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