276 Dr. L. Vegard on the X-Ray Spectra 



ductive capacity ought to vary in about the same way as 

 the quantity : 



*'(-£$> (29) 



where n is the quant-number and q the number of electrons 

 of the surface ring. 



Now we found that in order to get the observed typical 

 variation of the conductive capacity with atomic number 

 (Benedick's curve) we had to assume the quant-number n to 

 be constant for all elements belonging to the same period, or 

 for all elements falling between tvoo successive inert gases. 



On this assumption we got the right type of variation 

 of the conductive capacity for both the short periods (see 

 Paper I. fig. 4). But also for the two long periods (Ar-Kr) 

 and Kr-Xe) we get the right type of variation, when we 

 assume n constant inside each interval. Let us, e. (/., con- 

 sider the period between Ar and Kr. At first we get a 

 sudden fall of 1/cr with increasing q as we pass from K 

 to Ni. Then a new ring is formed which should produce 

 a sudden increase of 1/cr for the element Cu. In fact we 

 find a sudden increase of the conductive capacity for Cu 

 followed by a fall which is continued till the next period 

 sets in with Kr. 



There is, however, an apparent disagreement with regard 

 to the magnitude of the conductive capacity. 



The formula (29) would give both for K and Cu the same 

 value of 1/cr, while the observed conductive capacity is 

 very much smaller for Cu. I think, however, that the 

 smaller value in the case of Cu is just what we may expect 

 from theory. The expression for 1/cr given in equation (29) 

 is deduced on the assumption that the effect of the internal 

 electrons is the same as if they were placed at the centres. 



Now the radius of the surface ring is determined by the 

 equation (Paper I., equation 25) : 



n 2 

 a = a *7T~fC> ( 30 ) 



where a H is the radius of the surface ring of hydrogen. 

 When we pass an inert gas — Ar, say — we shall have an 

 increase of a from the two causes : increase of n and 

 diminution of q. When, however, we pass from Ni to Cu 

 we have a relatively smaller increase of a because now the 

 quant-number is unaltered. Now this comparatively much 

 smaller jump with regard to the radius which is found for 

 Cu may account for its smaller conductive capacity as 

 compared with that of K. 



For chemically related elements q is the same, and the 



