712 Mr. H. G. J. Moseley on the 



regularities would at once disappear. We can therefore 

 conclude from the evidence of the X-ray spectra alone, with- 

 out using any theory of atomic structure, that these integers 

 are really characteristic of the elements. Further, as it is 

 improbable that two different stable elements should have 

 the same integer, three, and only three, more elements are 

 likely to exist between Al and Au. As the X-ray spectra 

 of these elements can be confidently predicted, they should 

 not be difficult to find. The examination of keltium * would 

 be of exceptional interest, as no place has been assigned to 

 this element. 



Now "Rutherford t has proved that the most important con- 

 stituent of an atom is its central positively charged nucleus, 

 and van den Broek % has put forward the view that the 

 charge carried by this nucleus is in all cases an integral 

 multiple of the charge on the hydrogen nucleus. There is 

 every reason to suppose that the integer which controls the 

 X-ray spectrum is the same as the number of electrical units 

 in the nucleus, and these experiments therefore give the 

 strongest possible support to the hypothesis of van den Broek. 

 Soddy § has pointed out that the chemical properties of the 

 radio-elements are strong evidence that this hypothesis is 

 true for the elements from thallium to uranium, so that its 

 general validity would now seem to be established. 



From the approximate linear relation between v* and N 

 for each line we obtain the general equation 



V = K (N-6) 2 , 



where A and b are constants characteristic of each line. For 

 the K a. line 



A== (p — 22V0 and 6 = 1. 



For the L a line approximately 



A = (^ 2 ~~3 2 ) V ° and h = 1 '^' 



The fact that the numbers and arrangement of the lines in 

 the K and the L spectra are quite different, strongly suggests 

 that they come from distinct vibrating systems, while the 

 fact that b is much larger for the L lines than for the K lines 



* TJrbain, CM. clii. p. 141 (1911). 



t Rutherford, Phil. Mag-, xxi. p. 669 (1911), andxxvii. p. 488 (1914). 



% Van den Broek, Fhys. Zeit. xiv. p. 82 (1913), and ' Nature/ Nov. 27, 

 Dec. 25, 1913, March 5, 1914. 



§ Soddy, Jahrbuch Had. imd. Elect, x. p. 193 (1913) ; ' Nature,' Dec. 4, 

 Dec. 18 (1913;. 



