624 Dr. F. W. Aston on the 



Table of Results. 



Minimum 



Element. Atomic Atomic number of Mass of isotopes 



number. weight. isotopes. in order of intensity. 



H 1 1-008 1 1-008 



He 2 309 1 4 



6 12-00 1 '12 



N 7 14-01 1 14 



8 16-00 1 16 



Ne 10 20-20 2 20,22,(21) 



01 17 35-46 2 35,37,(39) 



A 18 39-9 (2) 40,(36) 



Kr 36 82-92 6 84,86,82,83,80,78 



X 54 130-2 5 (128,131,130,133,135) 



Hg .„ 80 200-6 (5) (197-200,202,204) 



[Numbers in brackets provisional only.] 



The Whole-number Rule. 



The most important generalization yielded by these experi- 

 ments is the remarkable fact that (with the exception of Hi, 

 H 2 , and H 3 ) all masses atomic or molecular, element or 

 compound, so far measured are whole numbers within the 

 accuracy of experiment. It is naturally premature to state 

 that this relation is true for all elements, but the number and 

 variety of those already exhibiting it makes the probability 

 of this extremely high-. 



On the other hand, it must not be supposed that this would 

 imply that the whole-number rule holds with mathematical 

 exactness, but only that the approximation is of a higher 

 order than that exhibited by the ordinary chemicaj com- 

 bining weights and is quite close enough to allow of a theory 

 of atomic structure far simpler than those put forward in the 

 past ; for such theories were forced to attempt the explana- 

 tion of fractions which now appear to be merely fortuitous 

 statistical effects due to the relative quantities of the isotopic 

 constituents. 



Thus one may now suppose that an elementary atom of 

 mass m may be changed to one of mass m + 1 by the addition 

 of a positive particle and an electron. If both enter the 

 nucleus an isotope results, for the nuclear charge is unaltered. 

 If the positive particle only enters the nucleus, an element of 

 next higher atomic number is formed. In cases where both 

 forms of addition give a stable configuration, the two elements 

 will be isobares. 



The electromagnetic theory of mass asserts that mass is not 

 generally additive but only becomes so w r hen the charges 



