120 



SCIENCE 



[N. S. Vol. XL. No. 1021 



the resulting Eontgen rays from a crystal 

 and measured the wave-lengths of one or 

 other of the principal {E or L, hard or 

 soft) radiations. 



In this manner he found 



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 ele- 

 ments not yet found by the chemists. 

 These experimental results bear out well a 

 view first propounded by van den Broek, 

 that each element has an atomic number, 

 an integer representing its place in the 

 periodic table (H 1, He 2, Li 3, Be 4, Bo 5, 

 C 6, and so forth). The atomic weight is 

 not an exact integer, nor of such funda- 

 mental 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 (Ra B), 

 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 spec- 

 trum, 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. 



13. All of these results are in harmony 

 with the wonderful advances in radio- 

 chemistry due to Soddy, Fajans, Von 

 Hevesy and others. It has been found that 

 when a radiant emits an alpha particle or 

 helium nucleus, the chemical properties 

 of the newly formed radiant differ from the 

 old. A fresh element is formed, a different 

 valency results, and the new radiant, rela- 

 tive to the old, is two columns to the left 

 in the periodic table. The atomic number 

 has decreased 2, and the atomic weighlE 

 about 4. But when a radiant ejects a heta 

 particle or electron, again there is a new 

 radiant with different valency and chemical 

 properties, but there is a move of one 

 column to the right in the periodic table; 

 a gain of one in the atomic number and no 

 change in the atomic weight. 



A brief example of the whole scheme 

 applicable to all radiants is given below: 



In the case of these radiants Ur 1 ejects 

 an a particle and gives rise to UrXl. 

 The latter and Ur X 2, respectively, emit a 

 p particle. 



It should be added that the short-lived 

 product UrX2 or "brevium" was dis- 

 covered by this theory, after it had been 

 formulated from the known behavior of 

 other radiants. 



It will be seen that Uranium 1 and 2 are 



