A HISTORY OF SCIENCE 



few hours, and has to be replaced by a fresh supply 

 from the non-radio-active thorium." n 



If Professor Thompson's view be correct, the amount 

 of potential energy inherent in the atom must be 

 enormous. 



Radio-Activity and the Structure of the Atom 



But whatever the source of the energy displayed by 

 the radio-active substances, it is pretty generally 

 agreed that the radio-activity of the radio-elements 

 results in the disruption of their atoms. Since all sub- 

 stances appear to be radio-active in a greater or less 

 degree, it would seem that, unless there be a very gen- 

 eral distribution of radio-active atoms throughout all 

 substances, all atoms must be undergoing disruption. 

 Since the distribution of radio-active matter throughout 

 the earth is so great, however, it is as yet impossible 

 to determine whether this may not account for the 

 radio-activity of all substances. 



As we have just seen, recent evidence seems to point 

 to the cause of the disruption of radio-active atoms as 

 lying in the atoms themselves. This view is quite in 

 accord with modern ideas of the instability of certain 

 atoms. It has been suggested that some atoms may 

 undergo a slower disintegration without necessarily 

 throwing off part of their systems with great velocity. 

 It is even possible that all matter may be under- 

 going transformation, this transformation tending to 

 simplify and render more stable the constituents of the 

 earth. The radio-active bodies, however, are the only 

 ones that have afforded an opportunity for studying 

 this transformation. In these the rapidity of the 



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