SCIENTIFIC HYPOTHESIS 249 



workers in this subject, namely, that radioactivity is 

 an atomic phenomenon. It is not molecular decompo- 

 sition. They declared that the radioactive substances 

 must be undergoing a spontaneous transformation. 

 The daring nature of this hypothesis and its likeli- 

 hood to revolutionize physical science is brought home 

 to one by recalling that three decades previously an 

 eminent physicist had said that "though in the 

 course of ages catastrophes have occurred and may 

 yet occur in the heavens, though ancient systems 

 may be dissolved and new systems evolved out of 

 their ruins, the molecules [atoms] out of which these 

 systems are built the foundation stones of the 

 material universe remain unbroken and unworn." 

 In 1903 Rutherford and Soddy stated definitely 

 their hypothesis, generally known as the " Transfor- 

 mation Theory," that the atoms of radioactive sub- 

 stances suffer spontaneous disintegration, a process 

 unaffected by great changes of temperature (or by 

 physical or chemical changes of any kind at the dis- 

 posal of the experimenter) and giving rise to new 

 radioactive substances differing in chemical (and 

 physical) properties from the parent elements. The 

 radiations consist of a particles (atoms of helium 

 minus two negative electrons), /3 particles, or elec- 

 trons (charges of negative electricity), and 7 rays, of 

 the nature of Rontgen rays and light but of very much 

 shorter wave length and of very great penetrating 

 power. It is by the energy inherent in the atom of the 

 radioactive substance that the radiations are ejected, 

 sometimes, in the case of the 7 rays with velocity 

 sufficient to penetrate two feet of lead. It is through 

 these radiations that spontaneous transformation 



