xvin THE CLASSIFICATION OF THE ELEMENTS 493 



There are, however, two vacant places, 84 and 85, between 

 Bi(83) and Nt(86), and three others, 87, 89, 91, between 

 Nt(86), Ra(88), Thfeo), 11(92), in a region in which the 

 atomic numbers have not yet been determined by experi- 

 ment. The total number of vacancies between hydrogen 

 and uranium is thus increased to nine. 1 



The existence of two light gases, "coronium" and 

 " nebulium," between hydrogen and helium has been sug- 

 gested by Rydberg (see Phil. Mag., July, 1914, 28, 139) on 

 the following grounds. The two short periods, from Li to 

 Ne and Na to Ar, contain 2 x 8 = 4 2 elements. The two 

 long periods, from K to Kr and Rb to Xe contain 2 x 18 = 6 2 

 elements. These should be followed by two very long periods 

 containing 2 x 32 = 8 2 elements, of which 27 out of 32 are 

 known in the range from Cs to Nt, and 3 beyond. On 

 the other hand, the two short periods should be preceded by 

 periods containing 2 x 2 = 2 2 elements, so that helium would 

 be the fourth 2 element instead of the second. 



The existence of a series of integral atomic numbers 

 proves " that there is in the atom a fundamental quantity, 

 which increases by regular steps as we pass from one 

 element to the next. This quantity can only be the 

 charge on the central positive nucleus" (Moseley 

 Phil. Mag., 1913, 26, 1031). The atomic weights are 

 determined mainly by the atomic numbers, but there is 

 evidently some secondary factor at work which may modify 

 the atomic weight by at least a unit. Thus in the two short 

 periods the atomic weights are just twice the atomic numbers 

 in the case of He, C, N, O, Ne, S ; but they are one unit 



1 Not counting the hypothetical gases " coronium " and " nebulium" 

 of atomic weight perhaps less than hydrogen. 



2 On these grounds Rydberg suggests that the atomic numbers should 

 be converted into ORDINALS by adding two units to all the elements 

 out hydrogen (Phil. Mag., July, 1914, 28, 144). This would not affect 

 Moseley's data, but measurements of the scattering of X-rays by gases 

 .ndicate consecutive numbers for hydrogen and helium (Phil. Mag., Oct. 

 1914, 28, 631); this difficulty could be overcome by placing the two 

 hypothetical gases before hydrogen instead of after. 



