Ernest Rutherford, Henry Moseley 185 



of investigation, and the result proved of the highest value. 

 The wave-lengths to be measured are less than the thousandth 

 part of that of visible rays,' and in that region the arrange- 

 ment of the lines was found to be the same for all elements ; 

 but proceeding from lower to higher atomic weights, the 

 spectrum was bodily displaced by a definite amount towards 

 the shorter wave-lengths. To see the full bearing of this 

 investigation, we must refer to the theory which Rutherford 

 had formed on the constitution of atoms, based mainly on 

 his experiments on the scattering of a particles by molecules 

 of matter. According to that theory, each atom possesses a 

 positively charged nucleus of exceedingly small dimensions. 

 The nucleus is made up of definite numbers of unit charges, 

 and if we arrange the elements in order of their atomic 

 weights, it is natural to suppose that the total charge 

 increases by one unit as we pass from one element to the next. 

 We may take the atomic number (meaning the number of 

 charges) as the characteristic of each element, and deal, 

 therefore, with figures which are successive integers, rather 

 than with the irregularly increasing numbers representing the 

 atomic weights. Moseley 's experiments prove that the high 

 frequency spectrum of the elements which he examined is 

 completely defined by the atomic number. It may be antici- 

 pated that this will prove to be the foundation of a new and 

 more precise chemistry, as other properties will be certain 

 to be intimately connected with the forces which regulate the 

 spectra. In confirmation of this, it may be stated that 

 Moseley in fixing the atomic number had to invert the order 

 in the case of potassium and argon, and that of cobalt and 

 nickel, and in both instances it is found that the chemical 

 properties agree with the spectroscopic evidence, and not 

 with that of the order of atomic weights. 



Moseley's results, while showing that all elements can be 

 placed in a certain definite order almost identical with that 

 of the atomic weights, allow us also to discover the gaps 

 which we may confidently expect to see filled up by hitherto 

 undiscovered elements. Eighty-three are known at present 

 and Moseley's table of results shows nine gaps between 

 argon and the heaviest of the metals, uranium. The total 

 number of elements reached, when the gaps are filled, will be 



