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XXXIX. The Constitution and Stability of Atom Nuclei . (A 

 Contribution to the Subject of Inorganic Evolution.) By 

 William D. Harkins, Ph.D., Professor of Physical 

 Chemistry in the University of Chicago*. 



i 



[Plate XII.] 



N a series of papers, the first of which was published in 

 1915, the writer has endeavoured to show that much 

 may be learned in regard to the stability, and also the 

 constitution of atom nuclei, by a careful study of the relative 

 abundance of the different atomic species, together with the 

 atomic weight and number relations, provided these are 

 consistently compared with what is already known in regard 

 to the corresponding relations among the radioactive atomic 

 species. The purpose of the present paper is to give evidence 

 concerning the relations already developed, which has been 

 obtained during the last year and a half through the discovery 

 of numerous new atomic species (isotopes), and to show that 

 the most important of these relations are even now securely 

 founded upon an experimental basis. That this is true in the 

 present incomplete state of our knowledge with, respect to 

 isotopes is due to the fact that while only relatively few of 

 the possible isotopes have been discovered, nevertheless 

 practically all of the most abundant atomic species are now 

 known. 



In considering the problem of atom building it will be 

 necessary to consider the nucleus alone, and not the sur- 

 rounding system of planetary electrons, since it seems 

 evident that if a nucleus becomes separated from these 

 electrons, as it may by a high speed collision with an alpha 

 particle, a new planetary electron system is quickly formed 

 by the picking up of electrons from the surrounding space 

 as soon as the speed of the nucleus is sufficiently reduced f. 



Note added Feb. 28. — To-day, just as the writer was about to mail 

 the present paper, lie found in a copy of tliis Magazine a paper by 

 Professor Orme Masson, in which there are certain features in common 

 with the one here submitted, although approached from a very different 

 point of view. The number n which he uses is the same as the isotopic 

 number of this paper. It should be pointed out, however, that the 

 writer had suggested the use of half of the values of n in a paper 

 presented to the 'Physical Review' in 1919 (xv. p. 78 (1920)), and used 



* Communicated by Prof. Sir E. Rutherford, F.R.S. 

 f The alpha particle itself is, presumably, the most frequently occurring 

 nucleus without the accompaniment of planetary electrons. 



Phil. Mag. S. 6. Vol. 42. No. 249. Sept. 1921. Y 



