192 ANNUAL REPORT SMITHSONIAN INSTITUTION, 1921. 



not yet analyzed are metals, Dempster's method is likely to yield 

 enormously important results in the future. A complete list of the 

 isotopes of the nonradioactive elements so far discovered is given in 

 the following table : 



Table of elements and isotopes. 



Masses of isotopes in order 

 of intensity. 



1.008. 



4. 



7,0. 



9. 



11, 10. 



12. 



14. 



16. 



19. 



20, 22 (21). 



23. 



24, 25, 26. 



28, 29 (30). 



31. 



32. 



35, 37 (39). 



40, 36. 



39, 41. 



58, 60. 



75. 



79, 81. 



84, 86, 82, 83, 80, 78. 



85, 87. 

 127. 



129, 132, 131, 134, 136(128,130?). 



133. 



(197-200), 202, 204. 



By far the most important general result of these investigations 

 is that, with the exception of hydrogen, the weights of the atoms of 

 all the elements measured, and therefore almost certainly of all ele- 

 ments, are whole numbers to the accuracy of experiment. In the 

 majority of the figures obtained by means of the mass-spectrograph 

 this accuracy is one part in a thousand. Of course the error ex- 

 pressed in fractions of a unit increases with the weight measured, 

 but with the lighter elements the divergence from the whole number 

 rule is extremely small. 



