1 2 SODD Y, Evolution of Matter by Radio-active Elements. 



strontium, and calcium. Between the three radio-elements 

 there is no chemical resemblance, and heavy atomic mass 

 is their sole common characteristic. These facts bear out 

 a view for which we shall find abundant additional evidence 

 as we proceed that the life of an atom, and therefore the 

 degree of radio-activity the corresponding element 

 exhibits, is not connected with its chemical properties. It 

 is not even connected with the atomic mass in the sense 

 that the greater the latter is the more unstable will the 

 atom be. Situated as we are, the observers for a short 

 time only of a process of evolution which has been 

 going on for indefinite ages, our knowledge of the 

 unstable atoms is necessarily limited by certain definite 

 ■considerations. These will be more fully considered in 

 the sequel. Of all possible groupings of the ' protyle,' 

 the atoms of the periodic law probably represent only a 

 selected number, viz., the forms with longest life, which 

 ■exist to-day because they have survived a long process 

 of evolution in which those physically unfit have 

 ■disappeared. The transition-forms already spoken of 

 represent on the other hand the elementary forms of 

 matter physically unfitted to survive, but which are brought 

 within our powers of knowledge because they constitute 

 the temporary halting places through which matter is 

 passing in a scheme of slow continuous evolution from the 

 heavier to the lighter forms. The original radio-active 

 elements may be described as the connecting links between 

 the two classes, partaking of the properties of each. 

 They are changing, but so excessively slowly that some 

 still survive. The point that must be made clear 

 here is that, so far as we know, the life of an atom 

 and its material properties are not connected in any 

 obvious way. This is brought out by a study of the 

 transition-forms. During: the whole existence of the 



