of Radium in the Periodic System. 



An 



The exponent is a proper fraction. This result may other- 

 wise be expressed thus : — 



The logarithms of the atomic weights and those of the dis- 

 tances ivhen plotted as coordinates lie on a straight line for a 

 chemically related group of elements. 



The following two figures illustrate this law. 



+.6 



Logarithm of the line-distance ("01 scale-division 

 =2*3 per cent, of the value). 



In fig. 1 it will be seen that among the alkalies potassium 

 alone falls slightly below the line passing through the re- 

 maining points. We do not mean thereby to suggest that 

 the directly determined atomic weight of potassium is in- 

 correct ; but it appears to us interesting that the straight-line 

 law is appreciably departed from precisely in the case of the 

 element whose atomic weight in the periodic system points 

 to an unknown disturbing cause, which produces the inversion 

 of the positions of argon and potassium. 



As regards boron, gallium, and indium, the radiation of 

 these elements in a magnetic field has not been investigated. 

 On the other hand, there is no room for doubt as regards the 

 line-pairs corresponding to aluminium and thallium. The 

 same applies to the alkali group, where only the two yellow 

 sodium lines have been investigated in a magnetic field. 



In fig. 2 is represented the same relation for Mg, Ca, Sr, 

 Ba, and Ra. The extrapolation gives for the atomic weight 

 of radium the value 258. Of course, the straight line may 

 be to some extent rotated and displaced without any great 

 departure from the points ; but the figure shows clearly that 

 the value 225 as determined by Madame Curie is considerably 

 removed from the straight line. 



In the following table the straight line is represented by a 

 formula, and the extrapolated value obtained by calculation. 



