RADIOACTIVITY 275 



This view constitutes an extension of ideas upon the 

 atomic nature of radioactivity, ideas which have led to the 

 discovery of radium. 



The theory of the transformation of radioactive elements 

 which has been developed by Rutherford and Soddy is now 

 generally adopted. 



According to this theory there exist no invariable radio- 

 active substances, but each of them undergoes in the course 

 of time a more or less rapid progressive destruction. 



A chemically simple radioactive substance is destroyed 

 in such a manner that the rapidity of the destruction is 

 proportional to the quantity present. Consequently this 

 quantity decreases according to a simple exponential law, 

 characterized by an invariable coefficient, which depends 

 on the nature of the substance and may serve to define it. 



These coefficients, or radioactive constants, seem inde- 

 pendent of experimental conditions and capable of consti- 

 tuting standards of time. 



The destruction of atoms may be compared to an explo- 

 sion, at which time fragments of the atoms may be thrown 

 off with or without an electric charge. 



The resulting products may be either inactive or en- 

 dowed with radioactivity, and in the latter case the newly 

 formed atom is not itself stable, but must submit to a new 

 disintegration at the end of a longer or shorter time. 



When the destruction of a form of ephemeral radio- 

 activity occurs according to a complex law, this law can 

 always be represented by an algebraic sum of exponential 

 terms, which is interpreted as a succession of simple trans- 

 formations of limited number. Experience has shown that 

 in this case the various terms of the series may be considered 

 as representing simple radioactive substances of which cer- 

 tain ones are capable of being separated. 



In pursuing the analysis of radioactive phenomena, we 

 succeed in establishing, starting from a primary substance, 

 a succession of terms which succeed one another in the 

 series of radioactive transformations. 



