[eve] THE CONSTITUTION OF THE ATOM 15 



no intrinsic difference between the great waves of wireless telegraphy, 

 several kilometres in length (10 6 cm), short electric waves, long heat 

 waves, visible light (10" 5 cm), ultraviolet waves, Rôntgen rays, 

 (1(T 8 cm), and gamma rays (10~ 9 ). 



The method of reflecting Rôntgen rays from a rocksalt or other 

 crystal has been applied by Moseley with marked success to the 

 determination of the nucleus charges of the atoms of most of the 

 elements. He bombarded the elements one after the other, by 

 electrons as cathode rays and reflected the resulting Rôntgen rays 

 from a crystal, and measured the wave lengths of one or other of the 

 principal (K or L, hard or soft) radiations. 



In this manner he found — 

 n = A(N— B) 2 . 

 where n is the frequency of vibration, N the nucleus electronic charge, 

 necessarily a whole number, and A and B are determined constants. 

 In this manner he has found the atomic numbers N of all the known 

 elements from aluminium 13 to gold 79. There appear to be but 

 two or three elements not yet found by the chemists. These experi- 

 mental results bear out well a view first propounded by van den 

 Broek, that each element has an atomic number, an integer represent- 

 ing its place in the periodic table (HI, He 2, Li 3, Be 4, Bo 5, C 6, and 

 so forth.) The atomic weight is not an exact integer, nor of such 

 fundamental character as the atomic number. There will be further 

 reference to this point later. 



(12). Rutherford has extended Moseley's method and results 

 to the crystal reflection of the gamma rays from a radiant (RaB) and 

 determined the wave lengths of many lines, in particular of the two 

 strongest. He has bombarded lead with Ra B rays and found the 

 wave lengths of the radiation stimulated in the lead. He found that 

 Radium B and lead gave the same spectrum, indicating that they have 

 the same atomic number, 82. Hence he deduced the atomic numbers 

 of all the radiants in the uranium-radium family. His results are 

 worth repeating. — 



Radiant Rays Atomic number Atomic weight 



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