CONTEMPORARY ADVANCES IN PHYSICS 



315 



spectroscopy have been lavished; and it turns out (according to 

 Bainbridge) to be 1.007775 ± .000035 to 16.00000. From another 

 part of the table of the elements, take caesium. This is one of the few 



80 



Z 



Fig. 7 — Diagram of the isotopes of the elements of atomic numbers over 60. 

 Lines connect isotopes belonging to one and the same radioactive series, most of 

 which are known by their radioactivity alone. The mass of the end-product of the 

 actinium series (AcD) is taken as 207 in accordance with Rutherford's opinion. 



analyzed elements which as yet has disclosed no trace of more than one 

 isotope, and the mass of this one amounts, in terms of "one sixteenth 

 of Oi«" to 132.93 ± 0.02. 



