Some Remarks on Radioactivity. 481 



probable — on the assumption of similar solubility relations. 

 From this will be understood the great difficulty of separating 

 these substances by crystallization, so that even after fre- 

 quently repeated re-crystallizations the corresponding radium 

 compound may contain more or less barium. The same holds 

 for the relation of radium to calcium as well as to strontium 

 and magnesium. 



The number 225 is in better correspondence with the 

 periodic system, in so far as it fits the gap between bismuth 

 and thorium in the proper column. According to the value 

 258, radium would have to be moved two rows further down 

 in the column Mg, Ca, Sr, Ba, and a number of new un- 

 occupied places would be created in the periodic system. 



On the other hand, Rutherford's remark may be adduced 

 in support of the higher value of the atomic weight. The 

 higher atomic weight is indicative of a more complicated 

 atomic structure, and therefore of an easier splitting up into 

 electrons. The element which gives off electrons most freely 

 should therefore also have the highest atomic weight. 



The radium line 4826* 14, which is the most prominent of 

 all in a Bunsen-flame, is also after resolution in a magnetic 

 field found to be analogous to the strongest Bunsen-flame 

 lines Ba 5535, Sr 4607, Ca 4226. All these lines become 

 resolved into triplets, which in the case of the elements con- 

 sidered consist of equidistant lines, the frequency scale being- 

 used. 



Hanover, Physical Institute of the Technical High School. 

 January 1903. 



XL VII. Some Remarks on Radioactivity. 

 To the Editors of the Philosophical ^Magazine. 

 Gentlemen, 



IN a recent number of the Comptes Rendu s, Jan. 26, 1903, 

 there appeared a paper by M. Henri Becquerel, entitled 

 ' Sur la deviabilite magnetique et la nature des certains 

 rayons emis par le radium et le polonium," and also one by 

 M. P. Curie " Sur la radioactivite induite et sur l'emanatioii 

 du radium," in the former of which certain criticisms of my 

 experimental methods, and in the latter of mv theoretical 

 views were made. 



I am very pleased that M. Becquerel, with the very active 

 material at his disposal, has confirmed in such a direct 

 manner by the photographic method the result- which I 

 had previously obtained by the electric method *, showing 



* Pkys. Zeit. No. 8, p. 235, Jan. 15 (1903) ; Phil. Mag. Feb. 1908. 



