RADIOACTIVITY 277 



Certain radioactive transformations are very slow ; e. g., 

 the destruction of uranium and of thorium. The effects of 

 the transformation are in these cases very insignificant 

 even after many years. 



But in the radioactive minerals these same transforma- 

 tions may have been produced during the process of time 

 of geologic epochs, and hence the study of the mineral per- 

 mits us to determine the relations of the radioactive bodies. 



Inversely, if one such relation is known we can deduce 

 from it the length of time during which the transformation 

 has taken place in an unaltered mineral. Thus by the 

 accumulation of helium occluded in minerals we can esti- 

 mate the age of the latter. 



If it were proved that all matter is more or less radio- 

 active, the relative proportions of the elements in the min- 

 erals could be studied with the view of making evident the 

 relations of genesis among the elements. To terminate this 

 brief review of the domain of radioactivity I will indicate 

 how great is the disengagement of energy by radioactive 

 bodies. 



Thus, for radium, whose rapidity of destruction is 

 approximately known (this rapidity is such that the radium 

 is half gone in about 2,000 years), the destruction of a 

 gram of matter involves the disengagement of a quantity 

 of heat equal to that which results from the combustion of 

 500 kilograms of carbon or 70 kilograms of hydrogen. 



We must conclude that the internal energy of an atom 

 is very great in relation to that which is brought into play 

 at the time of the combination of atoms in a molecule. This 

 fact is probably of a nature to explain the independence of 

 radioactive phenomena of experimental conditions. 



Among the attempts which have been made to influence 

 these phenomena, none has yet given a positive result. 

 Radioactivity results from the destruction of certain atoms, 

 and this destruction appears to us as a spontaneous 

 phenomenon. 



Experience shows also that everything takes place as if 



